The American Academy of Pediatrics recommends annual influenza immunization for all children with high-risk conditions who are 6 months of age and older, for all healthy children ages 6 through 59 months, for all household contacts and out-of-home caregivers of children with high-risk conditions and of healthy children younger than 5 years, and for all health care professionals.

To more fully protect against the morbidity and mortality of influenza, increased efforts are needed to identify and immunize all children at high risk and all healthy children ages 6 through 59 months and to inform their parents when annual immunizations are due. Previously unimmunized children who are at least 6 months of age but younger than 9 years should receive 2 doses of influenza vaccine, given 1 month apart, beginning as soon as possible on the basis of local availability during the influenza season. If children in this cohort received only 1 dose for the first time in the previous season, it is recommended that 2 doses be administered in the current season. This recommendation applies only to the influenza season that follows the first year that a child younger than 9 years receives influenza vaccine. A child who then also fails to receive 2 doses the next year should be given only 1 dose per year from that point on. Influenza vaccine should also continue to be offered throughout the influenza season, even after influenza activity has been documented in a community.

On the basis of global surveillance of circulating virus strains, the influenza vaccine may change from year to year; indeed, 1 of the 3 strains in the 2007–2008 vaccine is different from the previous year's vaccine. All health care professionals, influenza campaign organizers, and public health agencies should develop plans for expanding outreach and infrastructure to immunize all children for whom influenza vaccine is recommended. Appropriate prioritization of administering influenza vaccine will also be necessary when vaccine supplies are delayed or limited. Because the influenza season often extends into March, immunization against influenza is recommended to continue through late winter and early spring. Lastly, it is recommended that for the 2007–2008 season, and likely beyond, health care professionals do not prescribe amantadine or rimantadine for influenza treatment or chemoprophylaxis, because widespread resistance to these antiviral medications now exists among influenza A viral strains. However, oseltamivir and zanamivir can be prescribed for treatment or chemoprophylaxis, because influenza A and B strains remain susceptible.

The purpose of this statement is to update the current recommendations for routine use of influenza vaccine in children, which were originally published in a condensed format in April 2007.1  Highlights include (1) harmonization of the recommendation of the American Academy of Pediatrics (AAP) and the Centers for Disease Control and Prevention (CDC) that children younger than 9 years receive 2 doses of influenza vaccine in their second season of immunization if they only received 1 dose in the previous season; and (2) additional detail on the recommended storage, dosage, and administration of live-attenuated influenza vaccine (LAIV), including the recent licensure of LAIV for children as young as 2 years.

The continued expansion of the recommendations on influenza vaccine use among children in the United States is based on several considerations. Young children are at serious risk of influenza infection, hospitalization, and complications. The risk of influenza-associated hospitalization in healthy children younger than 24 months has been shown to be equal to or greater than the risk in previously recognized high-risk groups. Young children are at higher risk of hospitalization for influenza infection than are healthy 50- to 64-year-old adults, for whom routine immunization has been recommended since 2000.2  High rates of hospitalization of infants and young children during influenza seasons have been appreciated for decades35  (Table 1), but it has been difficult to determine the proportion of hospitalizations during influenza season attributable to respiratory syncytial virus and other respiratory tract viruses. Several studies have attempted to separate the relative contributions of respiratory syncytial virus and influenza to the hospitalization rate.68  Influenza hospitalization rates vary among studies (190–480 per 100000 population) because of differences in methodology and severity of influenza seasons. However, children younger than 24 months are consistently at substantially higher risk of hospitalization than are older children, and the risk of hospitalization attributable to influenza infection is highest in the youngest children. Children 24 through 59 months of age experience increased morbidity attributable to influenza illness, with increased rates of outpatient visits and use of antibiotics.712

Community studies indicate that school-aged children have had the highest rates of influenza infection, with annual attack rates as high as 42% demonstrated in prospective surveillance studies.6,13  During various annual influenza seasons, rates of outpatient visits attributable to influenza vary from 6 to 29 per 100 children.5  Influenza is also important in the pathogenesis of acute otitis media during influenza seasons.14  Annually, 3% to 5% of children are estimated to experience acute otitis media associated with influenza.6,15,16  Influenza and its complications have been reported to result in a 10% to 30% increase in the number of antimicrobial courses prescribed to children during the influenza season.5,6  Antecedent influenza infection is sometimes associated with development of pneumococcal and staphylococcal pneumonia in children.17,18  Methicillin-resistant staphylococcal community-acquired pneumonia, with a rapid clinical progression and a high fatality rate, has been reported in previously healthy children and adults with concomitant influenza infection.18  This, combined with the aforementioned high rates of influenza-associated hospitalization among children ages 6 through 23 months, indicates a need to include more young healthy children in annual immunization efforts.5,12

Well-designed studies support the recommendation of giving 2 doses rather than 1 to vaccine-naïve children who are at least 6 months of age but younger than 9 years (strong recommendation; evidence grade B [see Appendices 1 and 2 for definitions of evidence grades]).1921  Among children younger than 9 years who have never received influenza vaccine previously and who receive only 1 dose of influenza vaccine in their first year of vaccination, vaccine effectiveness is lower compared with children who receive 2 doses in their first year of being vaccinated. Unfortunately, the proportion of children who are fully immunized in their first year of influenza vaccination is low. In the 2005–2006 influenza season, only 1 of 5 children 6 through 23 months of age was fully immunized, and only 1 of 10 children needing 2 doses received both doses.22  More recent coverage data from 6 immunization information system sentinel sites (vaccine registries) indicated that coverage levels for the 2006–2007 influenza season did not increase at 5 of 6 sites compared with the 2005–2006 influenza season and remained below 28% at all 6 sites. Among 24- to 59-month-olds at the 6 sites, 1.9% to 18.1% were fully immunized during the 2006–2007 influenza season,23  the first season during which routine immunization of 24- to 59-month-olds was recommended.

Two recent, large retrospective studies of previously unimmunized children who had received 1 dose of trivalent inactivated influenza vaccine (TIV) determined that no substantial decrease had occurred in office visits related to influenza-like illness (ILI) compared with unimmunized children.21,24  Similar results were reported in a case-control study of children 6 to 59 months of age.25

Although the efficacy of TIV and LAIV vary depending on recipient age, dosage, and antigenic similarity between circulating and vaccine strains, both vaccines are cost-effective strategies for preventing influenza among children and their families when circulating and vaccine strains are identical. Both TIV and LAIV have been demonstrated to be effective in children and adults, but data directly comparing the efficacy or effectiveness of these 2 types of vaccines are limited, with studies having been conducted in a variety of settings and populations using several different clinical end points. Limited data suggest that LAIV, which has recently been approved for healthy individuals 2 years and older, provides greater protection than TIV for young children: LAIV provided 52% increased protection among children 6 to 71 months of age with recurrent respiratory tract infections.26  Another study conducted among children 6 to 59 months of age during the 2004–2005 influenza season demonstrated a 55% reduction in cases of culture-confirmed influenza among children who received LAIV, compared with those who received TIV.27

Although immunization against influenza early in life may not prevent all cases of infection, the current policy is expected to further decrease morbidity and mortality associated with this virus.28  It is hoped that broader routine influenza immunization will also reduce the financial costs attributable to influenza among people of all ages while improving the health of all children and families. Many consider this paradigm to represent a step toward universal annual influenza immunization in the United States.

Influenza is spread from person to person primarily by droplets of respiratory secretions expelled by coughing or sneezing but can also be spread by direct contact with influenza virus-contaminated surfaces. During community outbreaks of influenza, the highest attack rates occur among school-aged children. Secondary spread to adults and other children within a family is common. Incidence depends in part on immunity developed by previous experience (with natural disease) or recent influenza immunization with the circulating strain or a related strain. Immunity to the virus' surface antigens (hemagglutinin and neuraminidase) reduces the likelihood of infection and severity of disease if infection occurs.29  Antibody against 1 influenza virus type or subtype confers limited or no protection against another type or subtype of influenza. Furthermore, antibody to 1 antigenic variant of influenza virus might not completely protect against a new antigenic variant of the same type or subtype.30  Antigenic drift in the circulating strain(s) is a minor change in structure and is associated with seasonal epidemics. In temperate climates, seasonal epidemics usually occur during winter months. Antigenic shift (major changes in antigenic structure) is often associated with worldwide pandemics, because infection with previously circulating strains confers virtually no protection against the new strain of circulating virus.

Once influenza activity begins, community outbreaks can last 4 to 8 weeks or longer. People can spread infection 24 hours before symptoms manifest, peaking in viral shedding through nasal secretions during the first 3 days of the illness. Viral shedding directly correlates with the level of fever, however, and can be significantly prolonged in younger children and immunodeficient people.31  Because of the highly contagious nature of influenza, infected children easily spread the disease to adults and other children within a family or a community.28,31

Rates of infection are highest among children, but rates of serious illness and death are highest among people 65 years and older, children younger than 2 years, and people of any age who have medical conditions that place them at increased risk of having complications from influenza.3,3234  The attack rate among children has been estimated at 10% to 40% annually, with approximately 1% of infections resulting in hospitalization.6,14,3537  Rates of emergency department visits and hospitalizations attributable to influenza infection are especially high for otherwise healthy children younger than 5 years, with rates for children younger than 2 years substantially greater than rates for children 2 years and older.12,13,35  From 1979 to 2001, the estimated rate of influenza-associated hospitalizations in the United States among children younger than 5 years was approximately 108 per 100000 person-years.11  Recent population-based studies that have measured hospitalization rates for laboratory-confirmed influenza in young children have been consistent with studies that analyzed medical discharge data.6,9,3840  Annual hospitalization rates for laboratory-confirmed influenza in these studies decreased with age, ranging from 240 to 720 per 100000 healthy children younger than 6 months to 17 to 45 per 100000 for children 2 to 5 years of age. 6,3841  Estimated hospitalization rates for children with high-risk medical conditions are approximately 500 per 100000 children, and in 1 study, 37% of admissions occurred in children with medical conditions.7,8,11,40  Population-based studies among hospitalized children with laboratory-confirmed influenza have demonstrated that although the majority of hospitalizations are brief (≤2 days), 4% to 15% of children hospitalized with laboratory-confirmed influenza required treatment in the ICU, and 3% required mechanical ventilation.38,41  Among 1308 hospitalized children in 1 study, 80% were younger than 5 years, and 27% were younger than 6 months.41

There is also a high incidence of outpatient visits for influenza illness for children 23 to 59 months of age, with visit rates of 80 to 150 per 1000 children each year.712  Otitis media, nausea, and vomiting also are commonly associated with influenza illness.6,42,43  Influenza virus infections can cause primary influenza viral pneumonia; exacerbate underlying medical conditions (eg, pulmonary or cardiac disease); lead to secondary bacterial pneumonia, sinusitis, otitis, croup, or wheezing; or contribute to coinfections with other viral or bacterial pathogens.39,41,44  These specific complications have occurred at a rate between 0.2% and 25% in past years.35  The risks of hospitalization and morbidity associated with these complications are increased if children also have serious and chronic illnesses, such as hemoglobinopathies, bronchopulmonary dysplasia, asthma, cystic fibrosis, malignancy, diabetes mellitus, chronic renal disease, or congenital heart disease.

Deaths attributable to influenza are far less common in children than in the elderly. A study that modeled influenza-related deaths estimated that each year during the 1990s, an average of 92 deaths (0.4 deaths per 100000) occurred among children younger than 5 years, compared with 32651 deaths (98.3 per 100000) among adults 65 years or older.45  For both chronically ill and otherwise healthy children, however, fatal outcomes can occur. Of 153 laboratory-confirmed influenza-related pediatric deaths reported from 40 states during the 2003–2004 influenza season, 96 (63%) were children younger than 5 years and 61 (40%) were children younger than 2 years. Among the 149 children who died and for whom information on underlying health status was available, 100 (67%) did not have an underlying medical condition that was an indication for immunization at that time.46  In California during the 2003–2004 and 2004–2005 influenza seasons, 51% of children with laboratory-confirmed influenza who died and 40% of those who required admission to an ICU had no underlying medical conditions.10  These data indicate that although deaths are more frequent among children with risk factors for influenza complications, most pediatric deaths occur among children with no known high-risk conditions. In a single center throughout 3 consecutive influenza seasons, the mortality rate for children hospitalized with laboratory-confirmed influenza was 0.6% (2 of 325) and for all laboratory-confirmed influenza was 0.1% (2 of 1176).40

The annual number of influenza-related deaths among children reported to the CDC for the past 3 influenza seasons has ranged from 44 during 2004–2005 to 68 during 2006–2007.47  During the 2006–2007 season, among people younger than 18 years, of 53 patients 6 months or older for whom immunization status was known, 50 (94%) had not been immunized against influenza. Although influenza-related deaths are not common, it is felt that many of them are potentially preventable by immunization.

Although serious morbidity and mortality can result from influenza infection in any person, the risk of complications is increased among pregnant women,48  individuals with underlying chronic cardiopulmonary conditions,37,49  individuals with certain neuromuscular conditions,50  and immunocompromised people.51,52  Viral shedding can last for weeks or months, a much longer period of time than the average child or adult might experience. These groups are also more likely to experience symptoms on a more severe level and for a prolonged period of time.48,5355

The influenza virus generally requires an incubation period of 1 to 4 days, with an average of 2 days.56  When symptoms of the disease manifest, the typical influenza patient experiences a sudden onset of fever, chills or rigors, headache, malaise, diffuse myalgia, and nonproductive cough. Other common signs of the disease involve the respiratory tract, ranging from sore throat and nasal congestion to rhinitis and prominent coughing. More infrequently, conjunctival infection, abdominal pain, nausea, vomiting, and diarrhea have been reported in relation to influenza illness.35  Young children are less likely to report typical influenza symptoms. Adults who are infected with influenza virus can be contagious from the day before symptoms begin through the sixth day after onset of symptoms.56  Uncomplicated influenza illness typically resolves after 3 to 7 days for the majority of people, although cough and malaise can persist for more than 2 weeks.

Young children can also be infectious before symptoms begin and for as many as 10 days after onset of symptoms. Influenza is commonly characterized in children by otitis media, nausea, and vomiting in addition to the other general symptoms described above.6,42,43  In some children, influenza may appear as an upper respiratory tract infection or febrile illness with few respiratory tract symptoms. In infants, the disease can initially present signs similar to those of bacterial sepsis, high fever, or febrile seizures; studies have reported that up to 20% of children who are hospitalized for influenza infection experience febrile seizures.38,43,44,57  In addition, influenza illness has been known to occasionally develop into croup, bronchiolitis, or pneumonia.35  Although uncommon, other events that have been associated with influenza infection in children include encephalopathy, transverse myelitis, myositis, myocarditis, pericarditis, and Reye syndrome.43,44,58,59  Respiratory illnesses caused by influenza viruses are difficult to distinguish from illnesses caused by other respiratory pathogens on the basis of signs and symptoms alone. Sensitivity (ie, amount of false-negative results) and predictive value of clinical definitions can vary, depending on the extent of other respiratory pathogens circulating in the community at the same time and the local level of influenza activity.60  These results highlight the challenges of identifying influenza illness in the absence of laboratory confirmation.

Tables 2 and 3 summarize information on the 2 types of influenza vaccine used to immunize both children and adults (LAIV and TIV) and the age group in which each available preparation is licensed to be used. Both contain strains of influenza A subtypes H1N1 and H3N2 and influenza B, which are selected annually on the basis of the viruses anticipated for circulation during the upcoming influenza season. The 2007–2008 vaccine virus strains are A/Solomon Islands/3/2006 (H1N1)-like (new for this season), A/Wisconsin/67/2005 (H3N2)-like, and B/Malaysia/2506/2004-like antigens.47

TIV is an inactivated vaccine that contains killed viruses and, therefore, cannot produce an active virus infection. However, hypothetically, this killed vaccine might produce mild influenza-like symptoms by inducing some of the same cytokines associated with the known symptoms of influenza disease. TIV is administered intramuscularly to individuals who are 6 months and older, including those who are healthy and those with chronic medical conditions. LAIV is a live-attenuated vaccine that is administered intranasally and is currently licensed by the Food and Drug Administration for use in healthy individuals 2 through 49 years of age. LAIV has the potential to produce mild signs or symptoms related to influenza virus infection. Because viruses for both vaccines are grown in eggs, neither should be administered to anyone with known allergic reactions (ie, hives, angioedema, allergic asthma, and systemic anaphylaxis) to chicken, egg proteins, or any other component of the vaccines. Less severe or local manifestations of allergy to egg or feathers are not contraindications to administration of influenza vaccine.35

It has been consistently shown that seroconversion rates to TIV increase with the age of the child receiving immunization, ranging from 70% to 100% by adolescence.61,62  In 1 study in which 2 doses of TIV were administered to children between 6 and 24 months of age in 2 different influenza seasons, between 89% and 97% of the children in the 2 cohorts were considered seroprotected, as measured by a hemagglutinin-inhibi-tion (HAI) titer of more than or equal to 1:40 and/or a fourfold increase in antibody to influenza A(H1N1), A(H3N2), and B.63  Positive results have been similarly shown with the use of LAIV. Because LAIV is a live-attenuated vaccine, the resulting immune response is more likely to achieve a level of immunity that would be induced by natural influenza virus infection. Although studies have yet to determine precise humoral and cellular immunologic levels of protection by LAIV, HAI antibodies in serum, immunoglobulin A in nasal secretions, T-lymphocyte responses, and interferon production have all been correlated with LAIV protection from influenza infection.29,64

For immunocompromised patients, response to TIV varies depending on the degree of immunosuppression. Most HIV-infected children and adults produce increased levels of antibody after immunization with TIV, but their absolute antibody concentrations are lower than those seen in healthy, immunized individuals.65,66  Children with cancer who are not receiving chemotherapy frequently, and children who have sickle cell disease, have also been found to achieve adequate HAI response to TIV immunizations.67,68

The efficacy (ie, prevention of illness among vaccine recipients in controlled trials) and effectiveness (ie, prevention of illness in populations receiving vaccine) of influenza vaccines depends primarily on the age and immunocompetence of the vaccine recipient, the degree of similarity between the viruses in the vaccine and those in circulation, and the outcome being measured. Influenza vaccine efficacy and effectiveness studies typically have multiple possible outcome measures, including the prevention of medically attended acute respiratory illness, prevention of laboratory-confirmed influenza illness, prevention of influenza or pneumonia-associated hospitalizations or deaths, seroconversion to vaccine strains, or prevention of seroconversion to circulating influenza virus strains.50  For children 6 months and older, sufficient antibody levels against influenza are usually developed after receiving TIV.6976  Antibody response may be lower among children who are already at risk of developing complications from influenza infection.77,78  One study involving children 6 to 24 months of age found that 89% of children seroconverted to all 3 vaccine strains given in the years during which the study took place. Vaccine efficacy was 67% against culture-confirmed influenza in these children, with vaccine strains matching the circulating influenza virus strains well.63  Another study performed with children 1 to 15 years of age also demonstrated the effectiveness of TIV, with subjects exhibiting effectiveness rates of 77% and 91% during years which included H3N2 and H1N1, respectively.62  Vaccine efficacy of 56% against influenza illness was documented among healthy children 3 to 9 years of age,49  and another study determined vaccine efficacy against influenza type B and A infections of 22% to 54% and 60% to 78% among children with asthma 2 to 6 years of age and 7 to 14 years of age, respectively.79  TIV has also been found to considerably decrease the incidence of influenza-attributable otitis media among young children,8082  although another study contradicts this finding.63

Results have also shown the efficacy and effectiveness of LAIV. One study conducted with healthy children 15 to 71 months of age found that when vaccine and circulating strains were well matched, efficacy rates were 93% for participants who received 2 doses of LAIV. Even when vaccine and circulating strains were not well matched, efficacy rates remained high at 85%. LAIV was also found to be 92% efficacious in preventing culture-confirmed influenza during this two-season study. Additional results of this study include a 27% reduction in febrile otitis media and a 28% reduction in otitis media with concomitant use of antibiotics.83  In a study that compares live-attenuated vaccines versus inactivated influenza vaccines in infants and young children, LAIV shows significantly better efficacy and safety than TIV for children between 12 and 59 months of age without a recent history of wheezing or severe asthma.27  Available studies suggest that LAIV shows better efficacy than TIV in young children against both strains contained within the vaccine and for drifted strains.

#### TIV

The most common symptoms associated with TIV administration are soreness at the injection site and fever. Fever, usually occurring 6 to 24 hours after immunization, affects approximately 10% to 35% of children younger than 2 years.84  Mild systemic symptoms, such as nausea, lethargy, headache, muscle aches, and chills can also occur with TIV injection.

Control of fever with acetaminophen or other appropriate antipyretics may be important in young children, because fever and other symptoms of influenza could exacerbate underlying chronic conditions. Children and adolescents with influenza should not receive aspirin or any salicylate-containing products because of the resulting increased risk of developing Reye syndrome.35  Parents need to be warned about proper use of all antipyretics.

#### LAIV

Prelicensure studies found no significant difference in rates of fever, rhinitis, or nasal congestion between LAIV immunization and placebo administration. Postlicensure studies indicate that among children immunized for the first time, fever and stuffy nose are more common in recipients of LAIV than among recipients of TIV. An increase in fever, runny nose, and nasal congestion was shown after the first dose, but not after the second dose when administered to children 15 to 71 months of age.85  However, researchers have observed a statistically significant increase in asthma or reactive airway disease in children 12 to 59 months of age after the first dose with LAIV.83  In another study, medically significant wheezing was more common within 42 days after the first dose of LAIV compared with TIV among previously unimmunized children 6 to 24 months of age, and hospitalization for any cause within 180 days of immunization was significantly more common among LAIV recipients 6 to 11 months of age.27  An additional study was conducted among more than 11000 children 18 months to 18 years of age, in which 18780 doses of vaccine were administered for 4 years. For children 18 months to 4 years of age, no increase was reported in asthma visits 0 to 15 days after immunization, compared with the preimmunization period. A significant increase in asthma events was reported 15 to 42 days after immunization, but only in vaccine year 1.86

LAIV shedding can occur after immunization, although the amount of detectable virus is less than occurs during natural influenza infection. In the rare instance when shed vaccine virus is transmitted to a nonimmunized contact, illness has not occurred. However, inactivated influenza vaccine is preferred for close contacts of very severely immunosuppressed people50  (recommendation; evidence grade D) rather than LAIV.

#### Guillain-Barré Syndrome

If there is an association between seasonal influenza vaccine and Guillain-Barré syndrome (GBS), the risk is very minimal, at no more than 1 to 2 cases per million doses. Although an increase in the number of cases of GBS was reported during the “swine flu” vaccine program of 1976,87  obtaining strong epidemiologic evidence for a possible limited increase in risk for a rare condition with multiple causes is difficult.50  GBS has an annual incidence of 10 to 20 cases per 1 million adults,88  and during the 1976 swine influenza vaccine program, 1 GBS case was reported per 100000 people immunized. The risk of influenza vaccine-associated GBS was higher among people 25 years or older than among people younger than 25 years.88  Whether influenza immunization specifically might increase the risk of recurrence of GBS is unknown. However, avoiding immunizing people who are not at high risk of severe influenza complications and who are known to have experienced GBS within 6 weeks after a previous influenza vaccine dose is prudent.50

#### HIV

Because past reports are conflicting, the issue of safety of TIV immunization for children and adults with HIV infection is uncertain. However, experts generally believe that the benefits of TIV influenza immunization for children with HIV infection far outweigh the risks.

#### Allergies

Children with known allergic reactions (eg, hives, angioedema, allergic asthma, or systemic anaphylaxis) to chicken or egg proteins should not receive these vaccines, because both TIV and LAIV are developed with embryonated hen eggs (recommendation; evidence grade D). However, less severe or local manifestations of allergy to egg or feathers are not contraindications to administration of influenza vaccine.35

The hospitalization costs for influenza among children in the United States are estimated to be $55 million per year.40 Several studies have suggested that the costs and benefits of immunizing children produce significant savings from health care and societal perspectives. In 1 study, the savings per immunized child ranged from$7.23 to $15.98 in any program of children up to 13 years of age, and an investment of$2156109 in immunization of children younger than 5 years was predicted to result in an estimated savings yield of $3424409 in health care costs, even with an assumed vaccine efficacy of only 60%.89 Other cost analyses have documented the considerable cost burden of illness among children. In a study of 727 children at a single medical center during 2000–2004, the mean total cost of hospitalization for influenza-related illness was$13159 ($39792 for patients admitted to an ICU and$7030 for patients cared for exclusively on the wards).90  Strategies that focus on immunizing children with medical conditions that confer a higher risk of influenza complications seem to be more cost-effective than a strategy of immunizing all children.91  The expenses of immunizing children of varying ages were estimated, comparing the costs between using TIV with those of LAIV; costs per quality-adjusted life-year saved increased with age for both vaccines. In 2003 dollars per quality-adjusted life-year, costs for routine immunization using TIV were $12000 for healthy children 6 to 23 months of age and$119000 for healthy adolescents 12 to 17 years of age, compared with $9000 and$109000 using LAIV, respectively.92  Other studies demonstrated that influenza immunization of young children generates considerable savings from a societal perspective, especially if the total costs of immunization are less than $30 per child and if immunizations can be administered in after-hours or weekend group settings so as to help parents not miss work for their children's immunization.9396 A recent review of research on the costs and benefits of immunizing children, household contacts, and those at high risk of morbidity and mortality from influenza complications97 suggests that the immunization of children has the potential to protect others in their homes and communities. However, because of limitations in the design or execution of several analyzed studies, this finding remains inconclusive. Results from a public survey on the cost associated with influenza disease provided the following estimates: when asked about their willingness to pay to prevent a hypothetical child from having an uncomplicated case of influenza, the median willingness-to-pay amount was$100 for a child 14 years of age and \$175 for a child 1 year of age.98

TIV is a split-virus vaccine made up of inactivated, disrupted virus particles administered intramuscularly into the anterolateral thigh of infants and young children and into the deltoid muscle of older children and adults. The benefits of protecting children against the known risks of influenza far outweigh the hypothetical risks associated with the small amounts of thimerosal in some currently available forms of influenza vaccine. Certain types of TIV can be obtained free of thimerosal, including single-dose Fluzone (Sanofi Pasteur, Swiftwater, PA) and Fluvirin (Novartis, Emeryville, CA), but the latter vaccine is not licensed for use in children younger than 4 years.

The cold-adapted LAIV formulation that is currently licensed in the United States must be shipped and stored at 2°C to 8°C.50,99  LAIV doses are administered intranasally, in a prefilled, single-use sprayer containing 0.2 mL of vaccine. A removable dose-divider clip is attached to the sprayer to administer 0.1 mL separately to each nostril. Although information on how concurrent administration of LAIV with other vaccines affects the safety or efficacy of either LAIV or the simultaneously administered vaccine has not been well studied, it is generally recommended that inactivated or live vaccines be administered simultaneously with LAIV. After administration of a live vaccine, at least 4 weeks should pass before another live vaccine is administered. LAIV does not contain thimerosal.

To ensure the development of sufficient protection against influenza, influenza vaccine should be given during the autumn of each year before the onset of influenza season, at the time specified in the yearly recommendations of the CDC's Advisory Committee on Immunization Practices (www.cdc.gov/flu). Traditionally, the recommended time ranges from the beginning of October to the end of January, unless vaccine supplies are available and sufficient to immunize people earlier in September. Influenza vaccine administration throughout the entire season is now recommended, as the influenza season extends well into March (recommendation; evidence grade C). Immunization throughout the season may still protect some individuals against late outbreaks of influenza (Fig 1) . In addition, there may be more than 1 peak of activity during an influenza season, so later immunization may still help protect from a later peak caused by a different strain of influenza virus that same season.

Compared with a regimen of 2 doses in the fall, spring-fall priming of young children engenders similar antibody responses when vaccine antigens are unchanged from 1 season to the next.21  Priming in this fashion does provide a degree of protection against ILI but with substantially lower efficacy compared with a regimen that provides 2 doses in the fall. One study conducted over 2 consecutive seasons in which the vaccine antigens did not change estimated 62% effectiveness against ILI for healthy children who had received 1 dose in the spring and a second the following fall, compared with 82% for those who received both doses in the fall.24  A study assessing protective antibody responses after 1 and 2 doses of vaccine among children 5 to 8 years of age who never were immunized previously indicated that children who received 2 doses were substantially more likely than those who received 1 dose to have a protective antibody response.20  The proportion who had a protective antibody response against the H1N1 antigen and the H3N2 antigen increased from 67% and 92%, respectively, after the first dose to 93% and 97%, respectively, after the second dose. However, 36% of children who received 2 doses did not have a protective antibody response to the influenza B antigen.20

Annual immunization against influenza is the preferred strategy for prevention of infection, but certain situations exist in which the use of antiviral agents is beneficial.35

Two classes of antiviral medications are currently available and felt to be safe and effective in children for the treatment or prophylaxis of influenza infections: the adamantanes (amantadine and rimantadine) and the neuraminidase inhibitors (oseltamivir and zanamivir).103  However, because recent studies have shown that the overwhelming majority (92%) of influenza A virus isolates are resistant to the adamantanes in the United States, using amantadine or rimantadine is not recommended for treatment or chemoprophylaxis of the influenza A strain until data are available on susceptibility of this year's influenza isolates (recommendation; evidence grade C).50,103  However, oseltamivir and zanamivir are antiviral therapies that can be prescribed (recommendation; evidence grade C), if necessary, because surveillance data indicate that influenza A and B strains have not shown clinically important levels of resistance. These topics are covered in greater detail in the recently published AAP clinical report “Antiviral Therapy and Prophylaxis for Influenza in Children.”103

• Children younger than 6 months.

• Children who have a moderate-to-severe febrile illness. Minor illnesses, with or without fever, do not contraindicate its use, particularly among children with mild symptoms of upper respiratory tract infection or allergic rhinitis.

• Children who have a history of hypersensitivity, including anaphylaxis, to eggs; to any previous influenza vaccine dose; or to any of the vaccine components.

• Children who have a history of GBS (recommendation; evidence grade C).

• Children Who Should Not Be Immunized With LAIV.

• Children younger than 2 years (recommendation; evidence grade B).

• Children who have a moderate-to-severe febrile illness.

• Children who received other live vaccines within the last 4 weeks.

• Children who have asthma, reactive airways disease, or other chronic disorders of the pulmonary or cardiovascular systems.

• Children who have underlying medical conditions, including metabolic disease, such as diabetes, renal dysfunction, and hemoglobinopathies.

• Children who have known or suspected immunodeficiency disease or are receiving immunosuppressive therapies.

• Children who are receiving aspirin or other salicylates.

• Children who have a history of GBS (recommendation; evidence grade C).

• Adolescents who are pregnant.

• Children who have a history of hypersensitivity, including anaphylaxis, to eggs; to any previous influenza vaccine dose; or to any of the vaccine components.

Consideration should be given to the potential risks and benefits of administering influenza vaccine to any child with known or suspected immunodeficiency. Precaution should also be taken when considering LAIV administration to people with minor acute illness, such as a mild upper respiratory tract infection with or without fever. Although the vaccine can most likely be given in this case, LAIV should not be delivered if nasal congestion will impede the delivery of the vaccine to the nasopharyngeal mucosa, until the congestion-inducing illness is resolved.64  In addition, TIV is the influenza vaccine of choice for any child living with a family member or household contact who is severely immunocompromised (ie, in a protected environment). The preference of TIV over LAIV for these individuals is because of the theoretic risk of infection in an immunocompromised contact of a LAIV-immunized child. As a precautionary measure, recently immunized people should restrict contact with severely immunocompromised (ie, in a protected environment) patients for 7 days after LAIV immunization, although there have been no reports of LAIV transmission between these 2 groups.

• Healthy children 6 through 59 months of age (recommendation; evidence Grade B).

• Children at high risk and adolescents with underlying medical conditions, including:

• Asthma or other chronic pulmonary diseases, such as cystic fibrosis (recommendation; evidence grade B).

• Hemodynamically significant cardiac disease.

• Immunosuppressive disorders or therapy.

• HIV infection.

• Sickle cell anemia and other hemoglobinopathies.

• Diseases requiring long-term aspirin therapy, such as juvenile idiopathic arthritis or Kawasaki disease (TIV only).

• Chronic renal dysfunction.

• Chronic metabolic disease, such as diabetes mellitus.

• Any condition that can compromise respiratory function or handling of secretions or can increase the risk of aspiration, such as cognitive dysfunction, spinal cord injuries, seizure disorders, or other neuromuscular disorders.

• Household contacts and out-of-home caregivers of children younger than 5 years and children who are at risk of all ages. Immunization of close contacts of children younger than 6 months may be particularly important, because these infants cannot be immunized (recommendation; evidence grade B).

• Children who required regular medical follow-up or hospitalization during the preceding year because of chronic metabolic diseases, such as diabetes mellitus; renal dysfunction; hemoglobinopathies; or immunodeficiency caused by medication or by HIV infection.

• Any female who will be pregnant during influenza season (TIV only).

In addition, immunization with either TIV or LAIV is recommended for the following individuals to prevent transmission of influenza to those at risk, unless contraindicated:

• Individuals 5 years and older.

• Healthy contacts and caregivers of other children or adults at high risk of developing complications from influenza infection (recommendation; evidence grade B).

• Close contacts of immunosuppressed individuals (TIV only if severely immunosuppressed).

• Health care workers or volunteers.

• Information about influenza surveillance is available through the CDC Voice Information System (influenza update, 888-232-3228) or at www.cdc.gov/flu.

Influenza vaccine schedules and effectiveness depend a great deal on how well vaccine strains match circulating virus strains each year. Research to further enhance the methods currently used to predict potential antigenic changes each year is important. Evaluations of the impact of influenza immunization programs must account for year-to-year variations in influenza attack rates, illness severity, hospitalization costs and rates, and vaccine effectiveness.

The AAP continues to review new immunization strategies to protect against influenza, including the possibility of expanding routine influenza immunization recommendations toward universal immunization or other approaches that will help greatly reduce the transmission of influenza. Despite the implementation of a universal influenza immunization campaign in Ontario and the subsequent increase of vaccine distribution and financial resources for this promotion, the incidence of influenza in this Canadian province has not decreased after the introduction of this program.104  Others feel these data are susceptible to various biases and have suggested that to evaluate universal influenza immunization program effectiveness, other established and available measures used in previous studies describing the epidemiology of influenza should be used instead of laboratory data.105  Additional analyses on the cost-effectiveness of expanding influenza immunization programs are indicated to better clarify and specify the economic and societal effects associated with immunization. This is especially prudent with the recommendation to immunize healthy children through 18 years of age, as is being proposed to decrease transmission and burden of disease to the entire population at risk of influenza morbidity and mortality. Any move toward universal annual influenza immunization in the United States increases the demand and potentially could reduce the cost to produce more influenza vaccine, which should also stabilize the market and give incentive for increased production capacities by vaccine manufacturers.

In addition, health care professionals and the public will benefit from continued education about annual influenza illness and vaccines. Research is necessary in identifying gaps in proposed plans for executing large-scale immunization programs. Particular attention must be paid to vaccine supply, distribution, implementation, and financing so as to determine and achieve realistic immunization goals for children and society each year.

Efforts should be dedicated toward building outreach and infrastructure to ensure an optimal distribution of vaccine so that more people are immunized. All health care professionals, influenza campaign organizers, and public health agencies should develop and refine their plans for expanding outreach and infrastructure to improve immunization rates of children with high-risk conditions for whom the vaccine is recommended and all healthy children 6 through 59 months of age. In addition, more support for programs that increase uptake of vaccine in pregnant women is needed. Appropriate prioritization of recipients of influenza vaccine should always be considered, especially when local vaccine supplies are delayed or limited.

Continued investigation of the safety, immunogenicity, and effectiveness of LAIV for young children is important. Additional studies of other special populations, such as patients who are receiving mild-to-moderate immunosuppression (eg, methotrexate, low-dose corticosteroids) also warrant additional consideration. Development of a safe, immunogenic vaccine for infants younger than 6 months would also be valuable. Lastly, efforts are being explored to improve the vaccine development process so as to allow for a shorter interval between identification of vaccine strains to be included each year and vaccine production. For example, the development of a tissue culture-based vaccine could increase production capacity and eliminate the contraindication for those with known allergic reactions to egg proteins.

Joseph A. Bocchini, Jr, MD, Chairperson

Henry H. Bernstein, DO

John S. Bradley, MD

Michael T. Brady, MD

Carrie L. Byington, MD

Penelope H. Dennehy, MD

Robert W. Frenck, Jr, MD

Mary P. Glode, MD

Harry L. Keyserling, MD

David W. Kimberlin, MD

Sarah S. Long, MD

Lorry G. Rubin, MD

Robert Bortolussi, MD

Richard D. Clover, MD

American Academy of Family Physicians

Marc A. Fischer, MD

Centers for Disease Control and Prevention

Richard L. Gorman, MD

National Institutes of Health

R. Douglas Pratt, MD

Food and Drug Administration

Anne Schuchat, MD

Centers for Disease Control and Prevention

Benjamin Schwartz, MD

National Vaccine Program Office

Jeffrey R. Starke, MD

American Thoracic Society

Carol J. Baker, MD

Red Book Associate Editor

Larry K. Pickering, MD

Red Book Editor

Edgar O. Ledbetter, MD

H. Cody Meissner, MD

Alison Siwek, MPH

Statement TypeDefinitionImplication
Strong recommendation The subcommittee believes that the benefits of the recommended approach clearly exceed the harms (or that the harms clearly exceed the benefits in the case of a strong negative recommendation) and that the quality of the supporting evidence is excellent (grade A or B).a Clinicians should follow a strong recommendation unless a clear and compelling rationale for an alternative approach is present.
Recommendation The subcommittee believes that the benefits exceed the harms (or that the harms exceed the benefits in the case of a negative recommendation), but the quality of evidence is not as strong (grade B or C). In some clearly identified circumstances, recommendations may be made on the basis of lesser evidence when high-quality evidence is impossible to obtain and the anticipated benefits outweigh the harms. Clinicians also should generally follow a recommendation but remain alert to new information and sensitive to patient preferences.
Option Either the quality of evidence that exists is suspect (grade D) or well-performed studies (grade A, B, or C) show little clear advantage to one approach versus another. Clinicians should be flexible in their decision making in regards to appropriate practice, although they may set boundaries on alternatives; patient preference should play a substantial influencing role.
No recommendation There is both a lack of pertinent evidence (grade D) and an unclear balance between benefits and harms. Clinicians should feel little constraint in their decision making and be alert to new published evidence that clarifies the balance of benefit versus harm; patient preference should play a substantial influencing role.
Statement TypeDefinitionImplication
Strong recommendation The subcommittee believes that the benefits of the recommended approach clearly exceed the harms (or that the harms clearly exceed the benefits in the case of a strong negative recommendation) and that the quality of the supporting evidence is excellent (grade A or B).a Clinicians should follow a strong recommendation unless a clear and compelling rationale for an alternative approach is present.
Recommendation The subcommittee believes that the benefits exceed the harms (or that the harms exceed the benefits in the case of a negative recommendation), but the quality of evidence is not as strong (grade B or C). In some clearly identified circumstances, recommendations may be made on the basis of lesser evidence when high-quality evidence is impossible to obtain and the anticipated benefits outweigh the harms. Clinicians also should generally follow a recommendation but remain alert to new information and sensitive to patient preferences.
Option Either the quality of evidence that exists is suspect (grade D) or well-performed studies (grade A, B, or C) show little clear advantage to one approach versus another. Clinicians should be flexible in their decision making in regards to appropriate practice, although they may set boundaries on alternatives; patient preference should play a substantial influencing role.
No recommendation There is both a lack of pertinent evidence (grade D) and an unclear balance between benefits and harms. Clinicians should feel little constraint in their decision making and be alert to new published evidence that clarifies the balance of benefit versus harm; patient preference should play a substantial influencing role.
a

See Appendix 2 for the definitions of evidence grades.

Source: American Academy of Pediatrics, Steering Committee on Quality Improvement and Management. Classifying recommendations for clinical practice guidelines. Pediatrics. 2004;114(3):874–877.

Well-designed randomized, controlled trials or diagnostic studies performed on a population similar to the guideline's target population
Randomized, controlled trials or diagnostic studies with minor limitations; overwhelmingly consistent evidence from observational studies
Observational studies (case-control and cohort design)
Expert opinion, case reports, or reasoning from first principles (bench research or animal studies)
Well-designed randomized, controlled trials or diagnostic studies performed on a population similar to the guideline's target population
Randomized, controlled trials or diagnostic studies with minor limitations; overwhelmingly consistent evidence from observational studies
Observational studies (case-control and cohort design)
Expert opinion, case reports, or reasoning from first principles (bench research or animal studies)

Source: American Academy of Pediatrics, Steering Committee on Quality Improvement and Management. Classifying recommendations for clinical practice guidelines. Pediatrics. 2004;114(3):874–877.

FIGURE 1

Month of peak influenza activity (%) from 1976 to 2007.

FIGURE 1

Month of peak influenza activity (%) from 1976 to 2007.

Close modal
FIGURE 2

Algorithm for determining recommended influenza immunization actions for children.

FIGURE 2

Algorithm for determining recommended influenza immunization actions for children.

Close modal
TABLE 1

Estimated Influenza-Associated Hospitalization Rates, Selected Studies

Study YearsPopulationAge GroupHospitalization Rates (Per 100 000 People)
In Previously Recognized High-Risk GroupNot in Previously Recognized High-Risk Group
1973–19937,35  Tennessee Medicaid 0–11 mo, 1–2 y, 3–4 y, 5–14 y 1900, 800, 320, 93 496 (6–11 mo) to 1038 (0–5 mo), 186, 86, 41
1974–199916  Vaccine clinic <2 y — 200–300
1992–19978  Health maintenance organizations 0–23 mo, 2–4 y, 5–17 y — 144–187, 0–25, 8–12
1968–197335  Health maintenance organization 15–44 y, 45–64 y, ≥65 y 56–110, 392–635, 399–518 23–25, 13–23
1969–199590  National hospital discharge data <65 y, ≥65 y — 20–42, 125–228
2000–200139  Two counties <1 y, 1 y, 2 to <5 y — 170, 50, 20
2001–200439,40  Large children's hospital ≤6 mo, 6–11 mo, 1 to <2 y, 2 to <3 y — 253, 113, 96, 36
2000–20048  Three counties ≤6 mo, 6–23 mo, 24–59 mo — 240, 60, 20
2003–200441  9 States ≤6 mo, 6–23 mo 311, 118 —
1994–2000100  Health maintenance organization 6–23 mo, 2–4 y 213, 142 51, 32
2000–200498,106  Large children's hospital 0–23 mo, 2–4 y, 5–11 y, 12–17 y — 416, 70, 19, 18
Study YearsPopulationAge GroupHospitalization Rates (Per 100 000 People)
In Previously Recognized High-Risk GroupNot in Previously Recognized High-Risk Group
1973–19937,35  Tennessee Medicaid 0–11 mo, 1–2 y, 3–4 y, 5–14 y 1900, 800, 320, 93 496 (6–11 mo) to 1038 (0–5 mo), 186, 86, 41
1974–199916  Vaccine clinic <2 y — 200–300
1992–19978  Health maintenance organizations 0–23 mo, 2–4 y, 5–17 y — 144–187, 0–25, 8–12
1968–197335  Health maintenance organization 15–44 y, 45–64 y, ≥65 y 56–110, 392–635, 399–518 23–25, 13–23
1969–199590  National hospital discharge data <65 y, ≥65 y — 20–42, 125–228
2000–200139  Two counties <1 y, 1 y, 2 to <5 y — 170, 50, 20
2001–200439,40  Large children's hospital ≤6 mo, 6–11 mo, 1 to <2 y, 2 to <3 y — 253, 113, 96, 36
2000–20048  Three counties ≤6 mo, 6–23 mo, 24–59 mo — 240, 60, 20
2003–200441  9 States ≤6 mo, 6–23 mo 311, 118 —
1994–2000100  Health maintenance organization 6–23 mo, 2–4 y 213, 142 51, 32
2000–200498,106  Large children's hospital 0–23 mo, 2–4 y, 5–11 y, 12–17 y — 416, 70, 19, 18

— indicates data not available.

(Adapted with permission from Centers for Disease Control and Prevention. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices, 2007. MMWR Recomm Rep. 2007;56[RR-6]:6).

TABLE 2

Comparison of LAIV and TIV

ElementLAIVTIV
Route of administration Intranasal spray Intramuscular injection
Type of vaccine Live virus Killed virus
Product Attenuated, cold-adapted Inactivated subvirion or surface antigen
No. of included virus strains 3 (2 influenza A, 1 influenza B) 3 (2 influenza A, 1 influenza B)
Vaccine virus strains updated Annually Annually
Frequency of administrationa Annually Annually
Approved age and risk groups Healthy people 2–49 y of age People ≥6 mo
Interval between 2 doses in children 4 wk 4 wk
Can be simultaneously administered with other vaccines Yesb Yesc
If not simultaneously administered,
Can be administered within 4 wk of another live vaccine No, prudent to space 4 wk apart Yes
Can be administered within 4 wk of an inactivated vaccine Yes Yes
ElementLAIVTIV
Route of administration Intranasal spray Intramuscular injection
Type of vaccine Live virus Killed virus
Product Attenuated, cold-adapted Inactivated subvirion or surface antigen
No. of included virus strains 3 (2 influenza A, 1 influenza B) 3 (2 influenza A, 1 influenza B)
Vaccine virus strains updated Annually Annually
Frequency of administrationa Annually Annually
Approved age and risk groups Healthy people 2–49 y of age People ≥6 mo
Interval between 2 doses in children 4 wk 4 wk
Can be simultaneously administered with other vaccines Yesb Yesc
If not simultaneously administered,
Can be administered within 4 wk of another live vaccine No, prudent to space 4 wk apart Yes
Can be administered within 4 wk of an inactivated vaccine Yes Yes
a

Two doses may be needed for children <9 years of age, depending on individual circumstances.

b

No data are available regarding effect on safety or efficacy.

c

TIV coadministration has been evaluated systematically only among adults with pneumococcal polysaccharide vaccine.

TABLE 3

Influenza Vaccines Licensed for Use in Different Age Groups—United States, 2007–2008 Season

VaccineTrade NameManufacturerDose/PresentationThimerosal Mercury Content (μg of Hg/0.5-mL dose)Age Group
Inactivated
TIV Fluzone Sanofi Pasteur 0.25-mL prefilled syringe 6–35 mo
0.5-mL prefilled syringe ≥36 mo
0.5-mL vial ≥36 mo
5.0-mL multidose vial 25 ≥6 mo
TIV Fluvirin Novartis (formerly Chiron) (Cambridge, MA) 0.5-mL prefilled syringe <1.0 ≥4 y
TIV Fluvirin Novartis (formerly Chiron) (Cambridge, MA) 5.0-mL multidose vial 24.5 ≥4 y
TIV Fluarix GlaxoSmithKline (Rixensart, Belgium) 0.5-mL prefilled syringe <1.25 ≥18 y
TIV FluLaval GlaxoSmithKline 5.0-mL multidose vial 25 ≥18 y
TIV Afluria CSL Limited (Parkville, Victoria, Australia) 0.5-mL prefilled syringe ≥18 y
5-mL multidose vial 24.5
Live-attenuated
LAIV FluMist MedImmune 0.2-mL sprayer 2–49 y
VaccineTrade NameManufacturerDose/PresentationThimerosal Mercury Content (μg of Hg/0.5-mL dose)Age Group
Inactivated
TIV Fluzone Sanofi Pasteur 0.25-mL prefilled syringe 6–35 mo
0.5-mL prefilled syringe ≥36 mo
0.5-mL vial ≥36 mo
5.0-mL multidose vial 25 ≥6 mo
TIV Fluvirin Novartis (formerly Chiron) (Cambridge, MA) 0.5-mL prefilled syringe <1.0 ≥4 y
TIV Fluvirin Novartis (formerly Chiron) (Cambridge, MA) 5.0-mL multidose vial 24.5 ≥4 y
TIV Fluarix GlaxoSmithKline (Rixensart, Belgium) 0.5-mL prefilled syringe <1.25 ≥18 y
TIV FluLaval GlaxoSmithKline 5.0-mL multidose vial 25 ≥18 y
TIV Afluria CSL Limited (Parkville, Victoria, Australia) 0.5-mL prefilled syringe ≥18 y
5-mL multidose vial 24.5
Live-attenuated
LAIV FluMist MedImmune 0.2-mL sprayer 2–49 y

Sources: American Academy of Pediatrics1  and Afluria [package insert]. CSL Limited, Parkville, Victoria, Australia; 2007.

The material contained in the attached document has been approved by the American Academy of Pediatrics but may not be released to the public or press until the embargo release date.

This policy statement was prepared in parallel with CDC recommendations and reports.50  Much of the background presented in this AAP report is based on the literature review, analyses of unpublished data, and deliberations of CDC staff in collaboration with the Advisory Committee on Immunization Practices Influenza Working Group, with liaison from the AAP.

1
American Academy of Pediatrics, Committee on Infectious Diseases. Prevention of influenza: recommendations for influenza immunization of children, 2006–2007.
Pediatrics.
2007
;
119
(4):
846
–851
2
Maciosek MV, Solberg LI, Coffield AB, Edwards NM, Goodman MJ. Influenza vaccination: health impact and cost effectiveness among adults aged 50 to 64 and 65 and older.
Am J Prev Med.
2006
;
31
(1):
72
–79
3
Glezen WP, Decker M, Joseph SW, Mercready RG Jr. Acute respiratory disease associated with influenza epidemics in Houston, 1981–1983.
J Infect Dis.
1987
;
155
(6):
1119
–1126
4
Glezen WP. Serious morbidity and mortality associated with influenza epidemics.
Epidemiol Rev.
1982
;
4
(1):
25
–44
5
Mullooly JP, Barker WH. Impact of type A influenza on children: a retrospective study.
Am J Public Health.
1982
;
72
(9):
1008
–1016
6
Neuzil KM, Zhu Y, Griffin MR, et al. Burden of interpandemic influenza in children younger than 5 years: a 25-year prospective study.
J Infect Dis.
2002
;
185
(2):
147
–152
7
Neuzil KM, Mellen BG, Wright PF, Mitchel EF Jr, Griffin MR. The effect of influenza on hospitalizations, outpatient visits, and courses of antibiotics in children.
N Engl J Med.
2000
;
342
(4):
225
–231
8
Izurieta HS, Thompson WW, Kramarz P, et al. Influenza and the rates of hospitalization for respiratory disease among infants and young children.
N Engl J Med.
2000
;
342
(4):
232
–239
9
Poehling KA, Edwards KM, Weinberg GA, et al. The underrecognized burden of influenza in young children.
N Engl J Med.
2006
;
355
(1):
31
–40
10
Louie JK, Schechter R, Honarmand S, et al. Severe pediatric influenza in California, 2003–2005: implications for immunization recommendations.
Pediatrics.
2006
;
117
(4). Available at: www.pediatrics.org/cgi/content/full/117/4/e610
11
Thompson WW, Shay DK, Weintraub E, et al. Influenza-associated hospitalizations in the United States.
JAMA.
2004
;
292
(11):
1333
–1340
12
Bourgeois FT, Valim C, Wei JC, McAdam AJ, Mandl KD. Influenza and other respiratory virus-related emergency department visits among young children.
Pediatrics.
2006
;
118
(1). Available at: www.pediatrics.org/cgi/content/full/118/1/e1
13
Glezen WP, Couch RB. Interpandemic influenza in the Houston area, 1974–76.
N Engl J Med.
1978
;
298
(11):
587
–592
14
Heikkinen T, Thint M, Chonmaitree T. Prevalence of various respiratory viruses in the middle ear during acute otitis media.
N Engl J Med.
1999
;
340
(4):
260
–264
15
Ruuskanen O, Arola M, Putto-Laurila A, et al. Acute otitis media and respiratory virus infections.
Pediatr Infect Dis J.
1989
;
8
(2):
94
–99
16
Chonmaitree T, Owen MJ, Patel JA, Hedgpeth D, Horlick D, Howie VM. Effect of viral respiratory tract infection on outcome of acute otitis media.
J Pediatr.
1992
;
120
(6):
856
–862
17
O'Brien KL, Walters MI, Sellman J, et al. Severe pneumococcal pneumonia in previously healthy children: the role of preceding influenza infection.
Clin Infect Dis.
2000
;
30
(5):
784
–789
18
Centers for Disease Control and Prevention. Severe methicillin-resistant Staphylococcus aureus community-acquired pneumonia associated with influenza–Louisiana and Georgia, December 2006–January 2007.
MMWR Morb Mortal Wkly Rep.
2007
;
56
(14):
325
–329
19
Englund JA, Walter EB, Fairchok MP, Monto AS, Neuzil KM. A comparison of 2 influenza vaccine schedules in 6- to 23-month-old children.
Pediatrics.
2005
;
115
(4):
1039
–1047
20
Neuzil KM, Jackson L, Nelson J, et al. Immunogenicity and reactogenicity of one versus two doses of trivalent inactivated influenza vaccine in vaccine-naïve 5–8-year-old children.
J Infect Dis.
2006
;
194
(8):
1032
–1039
21
Ritzwoller DP, Bridges CB, Shetterly S, Yamasaki K, Kolczak M, France EK. Effectiveness of the 2003–2004 influenza vaccine among children 6 months to 8 years of age, with 1 vs 2 doses.
Pediatrics.
2005
;
116
(1):
153
–159
22
Centers for Disease Control and Prevention. Influenza vaccination coverage among children aged 6–23 months–United States, 2005–06 influenza season.
MMWR Morb Mortal Wkly Rep.
2007
;
56
(37):
959
–963
23
Centers for Disease Control and Prevention. Influenza vaccination coverage among children aged 6–59 months–six immunization information system sentinel sites, United States, 2006–07 influenza season.
MMWR Morb Mortal Wkly Rep.
2007
;
56
(37):
963
–965
24
Allison MA, Daley MF, Crane LA, et al. Influenza vaccine effectiveness in healthy 6- to 21-month-old children during the 2003–2004 season.
J Pediatr.
2006
;
149
(6):
755
–762
25
Shuler CM, Iwamoto M, Bridges CB, et al. Vaccine effectiveness against medically attended, laboratory-confirmed influenza among children aged 6 to 59 months, 2003–2004.
Pediatrics.
2007
;
119
(3). Available at: www.pediatrics.org/cgi/content/full/119/3/e587
26
Ashkenazi S, Vertruyen A, Aristegui J, et al. Superior relative efficacy of live attenuated influenza vaccine compared with inactivated influenza vaccine in young children with recurrent respiratory tract infections.
Pediatr Infect Dis J.
2006
;
25
(10):
870
–879
27
Belshe RB, Edwards KM, Vesikari T, et al. Live attenuated versus inactivated influenza vaccine in infants and young children.
N Engl J Med.
2007
;
356
(7):
685
–696
28
Yogev R. Influenza vaccine confusion: a call for an alternative evidence-based approach.
Pediatrics.
2005
;
116
(5):
1214
–1215
29
Clements ML, Betts RF, Tierney EL, Murphy BR. Serum and nasal wash antibodies associated with resistance to experimental challenge with influenza A wild-type virus.
J Clin Microbiol.
1986
;
24
(1):
157
–160
30
Couch RB, Kasel JA. Immunity to influenza in man.
Annu Rev Microbiol.
1983
;
37
:
529
–549
31
Brownstein JS, Kleinman KP, Mandl KD. Identifying pediatric age groups for influenza vaccination using a real-time regional surveillance system.
Am J Epidemiol.
2005
;
162
(7):
686
–693
32
Monto AS, Kioumehr F. The Tecumseh Study of Respiratory Illness. IX. Occurrence of influenza in the community, 1966–1971.
Am J Epidemiol.
1975
;
102
(6):
553
–563
33
Barker WH. Excess pneumonia and influenza associated hospitalization during influenza epidemics in the United States, 1970–78.
Am J Public Health.
1986
;
76
(7):
761
–765
34
Barker WH, Mullooly JP. Impact of epidemic type A influenza in a defined adult population.
Am J Epidemiol.
1980
;
112
(6):
798
–811
35
American Academy of Pediatrics. Influenza. In: Pickering LK, Baker CJ, Long SS, McMillan JA, eds.
Red Book: 2006 Report of the Committee on Infectious Diseases
. 27th ed. Elk Grove Village, IL: American Academy of Pediatrics;
2006
:
401
–411
36
Glezen WP, Decker M, Perrotta DM. Survey of underlying conditions of persons hospitalized with acute respiratory disease during influenza epidemics in Houston, 1978–1981.
Am Rev Respir Dis.
1987
;
136
(3):
550
–555
37
Neuzil KM, Wright PF, Mitchel EF Jr, Griffin MR. The burden of influenza illness in children with asthma and other chronic medical conditions.
J Pediatr.
2000
;
137
(6):
856
–864
38
Dagan R, Hall CB. Influenza A virus infection imitating bacterial sepsis in early infancy.
Pediatr Infect Dis.
1984
;
3
(3):
218
–221
39
Iwane MK, Edwards KM, Szilagyi PG, et al. Population-based surveillance for hospitalizations associated with respiratory syncytial virus, influenza virus, and parainfluenza viruses among young children.
Pediatrics.
2004
;
113
(6):
1758
–1764
40
Ampofo K, Gesteland PH, Bender J, et al. Epidemiology, complications, and cost of hospitalization in children with laboratory-confirmed influenza infection.
Pediatrics.
2006
;
118
(6):
2409
–2417
41
Schrag SJ, Shay DK, Gershman K, et al. Multistate surveillance for laboratory-confirmed, influenza-associated hospitalizations in children, 2003–2004.
Pediatr Infect Dis J.
2006
;
25
(5):
395
–400
42
Ryan-Poirier K. Influenza virus infection in children.
Adv Pediatr Infect Dis.
1995
;
10
:
125
–156
43
Peltola V, Ziegler T, Ruuskanen O. Influenza A and B virus infections in children.
Clin Infect Dis.
2003
;
36
(3):
299
–305
44
Douglas R Jr Influenza in man. In: Kilbourne ED, ed.
Influenza Viruses and Influenza.
New York, NY: Academic Press Inc;
1975
:
395
–418
45
Thompson WW, Shay DK, Weintraub E, et al. Mortality associated with influenza and respiratory syncytial virus in the United States.
JAMA.
2003
;
289
(2):
179
–186
46
Bhat N, Wright JG, Broder KR, et al. Influenza-associated deaths among children in the United States, 2003–2004.
N Engl J Med.
2005
;
353
(24):
2559
–2567
47
Centers for Disease Control and Prevention. Update: influenza activity–United States and worldwide, 2006–07 season, and composition of the 2007–08 influenza vaccine.
MMWR Morb Mortal Wkly Rep.
2007
;
56
(31):
789
–794
48
Neuzil KM, Reed GW, Mitchel EF, Simonsen L, Griffen MR. Impact of influenza on acute cardiopulmonary hospitalizations in pregnant women.
Am J Epidemiol.
1998
;
148
(11):
1094
–1102
49
Clover RD, Crawford S, Glezen WP, Taber LH, Matson CC, Couch RB. Comparison of heterotypic protection against influenza A/Taiwan/86 (H1N1) by attenuated and inactivated vaccines to A/Chile/83-like viruses.
J Infect Dis.
1991
;
163
(2):
300
–304
50
Centers for Disease Control and Prevention. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP).
MMWR Recomm Rep.
2007
;
56
(RR-6):
1
–54
51
Neuzil KM, Reed GW, Mitchel EF Jr, Griffin MR. Influenza-associated morbidity and mortality in young and middle-aged women.
JAMA.
1999
;
281
(10):
901
–907
52
Lin JC, Nichol KL. Excess mortality due to pneumonia or influenza during influenza seasons among persons with acquired immunodeficiency syndrome.
Arch Intern Med.
2001
;
161
(3):
441
–446
53
Klimov AI, Rocha E, Hayden FG, Shult PA, Roumillat LF, Cox NJ. Prolonged shedding of amantadine-resistant influenza A viruses by immunodeficient patients: detection by polymerase chain reaction-restriction analysis.
J Infect Dis.
1995
;
172
(5):
1352
–1355
54
Englund JA, Champlin RE, Wyde PR, et al. Common emergence of amantadine- and rimantadine-resistant influenza A viruses in symptomatic immunocompromised adults.
Clin Infect Dis.
1998
;
26
(6):
1418
–1424
55
Boivin G, Goyette N, Bernatchez H. Prolonged excretion of amantadine-resistant influenza a virus quasi species after cessation of antiviral therapy in an immunocompromised patient.
Clin Infect Dis.
2002
;
34
(5);
e23
–e25
56
Cox NJ, Subbarao K. Influenza.
Lancet.
1999
;
354
(9186):
1277
–1282
57
Chiu SS, Tse CY, Lau YL, Peiris M. Influenza A infection is an important cause of febrile seizures.
Pediatrics.
2001
;
108
(4). Available at: www.pediatrics.org/cgi/content/full/108/4/e63.
58
McCullers JA, Facchini S, Chesney PJ, Webster RG. Influenza B virus encephalitis.
Clin Infect Dis.
1999
;
28
(4):
898
–900
59
Morishima T, Togashi T, Yokota S, et al. Encephalitis and encephalopathy associated with an influenza epidemic in Japan.
Clin Infect Dis.
2002
;
35
(5):
512
–517
60
Orenstein WA, Bernier RH, Hinman AR. Assessing vaccine efficacy in the field. Further observations.
Epidemiol Rev.
1988
;
10
(1):
212
–241
61
Gruber WC, Taber LH, Glezen WP, et al. Live attenuated and inactivated influenza vaccine in school-age children.
Am J Dis Child.
1990
;
144
(5):
595
–600
62
Neuzil KM, Dupont WD, Wright PF, Edwards KM. Efficacy of inactivated and cold-adapted vaccines against influenza A infection, 1985 to 1990: the pediatric experience.
Pediatr Infect Dis J.
2001
;
20
(8):
733
–740
63
Hoberman A, Greenberg DP, Paradise JL, et al. Effectiveness of inactivated influenza vaccine in preventing acute otitis media in young children: a randomized controlled trial.
JAMA.
2003
;
290
(12):
1608
–1616
64
Murphy BR, Nelson DL, Wright PF, Tierney EL, Phelan MA, Chanock RM. Secretory and systemic immunological response in children infected with live attenuated influenza A virus vaccines.
Infect Immun.
1982
;
36
(3):
1102
–1108
65
Tasker SA, O'Brien WA, Treanor JJ, et al. Effects of influenza vaccination in HIV-infected adults: a double-blind, placebo-controlled trial.
Vaccine.
1998
;
16
(9–10):
1039
–1042
66
Chadwick EG, Chang G, Decker MD, Yogev R, Dimichele D, Edwards KM. Serologic response to standard inactivated influenza vaccine in human immunogenicity virus-infected children.
Pediatr Infect Dis J.
1994
;
13
(3):
206
–211
67
Brown AE, Steinherz PG, Miller DR, et al. Immunization against influenza in children with cancer: results of a three-dose trial.
J Infect Dis.
1982
;
145
(1):
126
68
Glezen WP, Glezen LS, Alcorn R. Trivalent, inactivated influenza virus vaccine in children with sickle cell disease.
Am J Dis Child.
1983
;
137
(11):
1095
–1097
69
La Montagne JR, Noble GR, Quinnan GV, et al. Summary of clinical trials of inactivated influenza vaccine–1978.
Rev Infect Dis.
1983
;
5
(4):
723
–736
70
Oxford JS, Schild GC, Potter CW, Jennings R. The specificity of the anti-haemagglutinin antibody response induced in man by inactivated influenza vaccines and by natural infection.
J Hyg (Lond).
1979
;
82
(1):
51
–61
71
Gonzalez M, Pirez MC, Ward E, Dibarboure H, Garcia A, Picolet H. Safety and immunogenicity of a paediatric presentation of an influenza vaccine.
Arch Dis Child.
2000
;
83
(6):
488
–491
72
Wright PF, Cherry JD, Foy HM, et al. Antigenicity and reactogenicity of influenza A/USSR/77 virus vaccine in children: a multicentered evaluation of dosage and safety.
Rev Infect Dis.
1983
;
5
(4):
758
–764
73
Daubeney P, Taylor CJ, McGaw J, et al. Immunogenicity and tolerability of a trivalent influenza subunit vaccine (Influvac) in high-risk children aged 6 months to 4 years.
Br J Clin Pract.
1997
;
51
(2):
87
–90
74
Wright PF, Thompson J, Vaughn WK, Folland DS, Sell SH, Karzon DT. Trials of influenza A/New Jersey/76 virus vaccine in normal children: an overview of age-related antigenicity and reactogenicity.
J Infect Dis.
1977
;
136
(suppl):
731
–741
75
Negri E, Colombo C, Giordano L, Groth N, Apolone G, La Vecchia C. Influenza vaccine in healthy children: a meta-analysis.
Vaccine.
2005
;
23
(22):
2851
–2861
76
Jefferson T, Smith S, Demicheli V, Harnden A, Rivetti A, Di Pietrantonj C. Assessment of the efficacy and effectiveness of influenza vaccines in healthy children: a systematic review.
Lancet.
2005
;
365
(9461):
773
–780
77
Groothuis JR, Lehr MV, Levin MJ. Safety and immunogenicity of a purified haemagglutinin antigen in very young high-risk children.
Vaccine.
1994
;
12
(2):
139
–141
78
Park CL, Frank AL, Sullivan M, Jindal P, Baxter BD. Influenza vaccination of children during acute asthma exacerbation and concurrent prednisone therapy.
Pediatrics.
1996
;
98
(2 Pt 1):
196
–200
79
Sugaya N, Nerome K, Ishida M, Matsumoto M, Mitamura K, Nirasawa M. Efficacy of inactivated vaccine in preventing antigenically drifted influenza type A and well-matched type B.
JAMA.
1994
;
272
(14):
1122
–1126
80
Clements DA, Langdon L, Bland C, Walter E. Influenza A vaccine decreases the incidence of otitis media in 6- to 30-month-old children in day care.
Arch Pediatr Adolesc Med.
1995
;
149
(10):
1113
–1117
81
Heikkinen T, Ruuskanen O, Waris M, Ziegler T, Arola M, Halonen P. Influenza vaccination in the prevention of acute otitis media in children.
Am J Dis Child.
1991
;
145
(4):
445
–448
82
Ozgur SK, Beyazova U, Kemaloglu YK, et al. Effectiveness of inactivated influenza vaccine for prevention of otitis media in children.
Pediatr Infect Dis J.
2006
;
25
(5):
401
–404
83
Centers for Disease Control and Prevention. Using live, attenuated influenza vaccine for prevention and control of influenza.
MMWR Recomm Rep.
2003
;
52
(RR-13):
1
–8
84
Rennels MB, Meissner HC; Committee on Infectious Diseases. Reduction of the influenza burden in children.
Pediatrics.
2002
;
110
(6). Available at: www.pediatrics.org/cgi/content/full/110/6/e80.
85
Belshe RB, Gruber WC, Mendelman PM, et al. Efficacy of vaccination with live attenuated, cold-adapted, trivalent, intranasal influenza virus vaccine against a variant (A/Sydney) not contained in the vaccine.
J Pediatr.
2000
;
136
(2):
168
–175
86
Piedra PA, Gaglani MJ, Riggs M, et al. Live attenuated influenza vaccine, trivalent, is safe in healthy children 18 months to 4 years, 5 to 9 years, and 10 to 18 years of age in a community-based, nonrandomized, open-label trial.
Pediatrics.
2005
;
116
(3);
e397
–e407
87
Ropper AH. The Guillain-Barre syndrome.
N Engl J Med.
1992
;
326
(17):
1130
–1136
88
Schonberger LB, Bregman DJ, Sullivan-Bolyai JZ, et al. Guillain-Barre syndrome following vaccination in the National Influenza Immunization Program, United States, 1976–1977.
Am J Epidemiol.
1979
;
110
(2):
105
–123
89
Salo H, Kilpi T, Sintonen H, Linna M, Peltola V, Heikkinen T. Cost-effectiveness of influenza vaccination of healthy children.
Vaccine.
2006
;
24
(23):
4934
–4941
90
Keren R, Zaoutis TE, Saddlemire S, Luan XQ, Coffin SE. Direct medical costs of influenza-related hospitalizations in children.
Pediatrics.
2006
;
118
(5). Available at: www.pediatrics.org/cgi/content/full/118/5/e1321
91
Meltzer MI, Neuzil KM, Griffin MR, Fukuda K. An economic analysis of annual influenza vaccination of children.
Vaccine.
2005
;
23
(8):
1004
–1014
92
Prosser LA, Bridges CB, Uyeki TM, et al. Health benefits, risks, and cost-effectiveness of influenza vaccination of children.
Emerg Infect Dis.
2006
;
12
(10):
1548
–1558
93
Cohen GM, Nettleman MD. Economic impact of influenza vaccination in preschool children.
Pediatrics.
2000
;
106
(5):
973
–976
94
Luce BR, Zangwill KM, Palmer CS, et al. Cost-effectiveness analysis of an intranasal influenza vaccine for the prevention of influenza in healthy children.
Pediatrics.
2001
;
108
. Available at: www.pediatrics.org/cgi/content/full/108/2/e24
95
Riddiough MA, Sisk JE, Bell JC. Influenza vaccination.
JAMA.
1983
;
249
(23):
3189
–3195
96
Meltzer MI, Cox NJ, Fukuda K. The economic impact of pandemic influenza in the United States: priorities for intervention.
Emerg Infect Dis.
1999
;
5
(5):
659
–671
97
Connock M, Jordan R, Fry-Smith A, et al.
Influenza Vaccination of Children and Household Contacts for the Indirect Protection of Others: A Systematic Review of Clinical and Cost-effectiveness
. Department of Public Health and Epidemiology: University of Birmingham, Birmingham, United Kingdom;
2005
. Report No. 53
98
Prosser LA, Bridges CB, Uyeki TM, et al. Values for preventing influenza-related morbidity and vaccine adverse events in children.
Health Qual Life Outcomes.
2005
;
3
:
18
. Available at: www.hqlo.com/content/3/1/18. Accessed November 8, 2007
99
FluMist [package insert]. Gaithersburg, MD: MedImmune Vaccines Inc;
2007
100
O'Brien MA, Uyeki TM, Shay DK, et al. Incidence of outpatient visits and hospitalizations related to influenza in infants and young children.
Pediatrics.
2004
;
113
(3 Pt 1):
585
–593
101
Englund JA, Walter EB, Gbadebo A, et al. Immunization with trivalent inactivated influenza vaccine in partially immunized toddlers.
Pediatrics.
2006
;
118
(3). Available at: www.pediatrics.org/cgi/content/full/118/3/e579
102
Walter EB, Neuzil KM, Zhu Y, et al. Influenza vaccine immunogenicity in 6- to 23-month-old children: are identical antigens necessary for priming?
Pediatrics.
2006
;
118
(3). Available at: www.pediatrics.org/cgi/content/full/118/3/e570
103
American Academy of Pediatrics, Committee on Infectious Diseases. Antiviral therapy and prophylaxis for influenza in children.
Pediatrics.
2007
;
119
(4):
852
–860
104
Groll DL, Thomson DJ. Incidence of influenza in Ontario following the universal influenza campaign.
Vaccine.
2006
;
24
(24):
5245
–5250
105
Kwong JC, Stukel TA, McGeer AJ, Manuel DG. Appropriate measures of influenza immunization program effectiveness.
Vaccine.
2007
;
25
(6):
967
–969
106
Coffin SE, Zaoutis TE, Rosenquist AB, et al. Incidence, complications, and risk factors for prolonged stay in children hospitalized with community-acquired influenza.
Pediatrics.
2007
;
119
(4):
740
–748