In 1995, the United States was the first country to introduce varicella vaccination into its routine childhood immunization program. More than 25 years later, morbidity and mortality from chickenpox has declined substantially, but continuing efforts are needed to ensure vaccination coverage remains high.
Prior to vaccine introduction, varicella represented an important societal and medical health burden, affecting almost everyone during childhood. There were approximately 4 million cases a year in the United States, with 10,500-13,500 hospitalizations and 100-150 deaths. More than 90% of these cases, two-thirds of hospitalizations and about half of the deaths occurred in children.
Varicella infection during the first 20 weeks of pregnancy can lead to severe birth defects and complications for the fetus, known as congenital varicella syndrome. In addition, varicella-zoster virus (VZV), which causes varicella, remains dormant in the body and can reactivate to cause zoster (shingles). One in three people will suffer from shingles later in life.
Before the vaccine, pediatricians routinely saw serious cases of varicella. The biggest concern for these patients were complications such as secondary infections, especially invasive group A Streptococcus and pneumonia, or neurologic complications. Some children underwent long treatments with antibiotics and several surgeries to treat necrotizing fasciitis.
During the 1960s and ’70s, varicella became a feared illness among immunosuppressed children treated for leukemia or other cancers. Many developed severe or fatal varicella. During the 1980s, before effective HIV therapy was available, serious varicella cases were seen in immunodeficient infants with underlying HIV infection, some of whom died quicky from pneumonia triggered by varicella.
Effects of vaccination program
During the first 25 years of the U.S. vaccination program (1995-2019), the greatest decline in VZV disease has been among people younger than 21 years, with a 97% decrease in hospitalizations and 99% drop in varicella deaths. In this age group, varicella hospitalization has become extremely rare, and varicella deaths have been nearly eliminated.
While significant declines in disease have been seen in all age groups, an underappreciated benefit of the program is its impact on pediatric shingles. The risk of shingles is lower among both healthy and immunocompromised children (approximately 80% lower risk among healthy vaccinated children vs. unvaccinated children). It is anticipated that childhood varicella vaccination also will protect against shingles later in life by preventing infection with the wild-type virus and thus its dormancy, giving pediatricians the chance to protect patients across the lifespan.
While two doses of the vaccine are more than 90% effective at preventing varicella, breakthrough cases can occur. However, the symptoms of a breakthrough case usually are milder than among those who are unvaccinated, with fewer or no vesicles and mild or no fever.
Because of this milder presentation, breakthrough cases pose diagnostic challenges. For example, clinicians might suspect hand, foot and mouth disease and not consider varicella. To recognize a breakthrough case, clinicians should keep varicella in the differential diagnosis when seeing a vesicular or maculopapular rash.
Importance of vaccination
While varicella frequently is perceived as a benign disease of childhood, most pediatricians know it can be serious, affecting not just the individual but the entire family. It also can put people in the community who are immunocompromised or pregnant at risk.
Even one case of varicella, be it in a hospital or school, is disruptive. Parents lose income if they have to miss work, and those with the disease are at high risk of shingles later in life.
While antiviral treatment exists for varicella, it is effective only when administered early in the disease course and is recommended only for high-risk patients. Vaccination is the primary means of controlling this disease.
High vaccination coverage has been critical in reducing the varicella burden in the United States over the past 25 years. However, opportunities remain to increase coverage and reduce disease burden.
The COVID-19 pandemic caused delays in many routine vaccinations. Therefore, pediatricians should make every effort to ensure patients are up to date, including adolescents who have not received a second dose of varicella vaccine. Adolescent visits are one of the last chances to screen and vaccinate before adulthood, when disease usually is more severe and can cause devastating complications during pregnancy.
Thanks to a safe and effective routine vaccination program, varicella is rare in the United States. This is a public health victory. Pediatricians have been and continue to be on the front lines.
Dr. Romero is director of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention. He also is a member of the AAP Committee on Infectious Diseases. Dr. Kimberlin is editor of the AAP Red Book.
- A supplement in the Journal of Infectious Diseases summarizes data collected over the first 25 years of the U.S. varicella vaccination program.
- Centers for Disease Control and Prevention’s varicella webpage
- Information on varicella-zoster infections from the AAP Red Book
- Child and adolescent immunization schedule
- Information for parents from HealthyChildren.org on chickenpox vaccine