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Red Book Online Outbreaks: Measles

May 21, 2024

UPDATE: As of May 16, 2024, a total of 139 measles cases were reported by 21 jurisdictions: Arizona, California, Florida, Georgia, Illinois, Indiana, Louisiana, Maryland, Michigan, Minnesota, Missouri, New Jersey, New York City, New York State, Ohio, Pennsylvania, Vermont, Virginia, Washington, West Virginia, and Wisconsin.

There have been 10 outbreaks (defined as 3 or more related cases) reported in 2024, and 70% of cases (97 of 139) are outbreak-associated. For comparison, 4 outbreaks were reported during 2023 and 48% of cases (28 of 58) were outbreak-associated. For more information on the ongoing outbreak in Chicago, Illinois see the Chicago Department of Public Health Measles Update.

Vaccination Status of 139 Cases:

Unvaccinated or Unknown: 82%

One MMR Dose: 13%

Two MMR Doses: 6%


Age of 139 Cases:

Under 5 years: 45% (63 cases)

5-19 years: 22% (31 cases)

20+ years: 32% (45 cases)


Hospitalization by Age of 139 Cases:

54% of cases hospitalized (75 of 139 cases) for isolation or management of measles complications.
Under 5 years: 63% (40 of 63)
5-19 years: 39% (12 of 31)
20+ years: 51% (23 of 45)

On March 18, 2024, the Centers for Disease Control and Prevention (CDC) issued a Health Alert Network (HAN) Health Advisory to inform clinicians and public health officials of an increase in global and U.S. measles cases and to provide guidance on measles prevention for all international travelers aged ≥6 months and all children aged ≥12 months who do not plan to travel internationally. Measles (rubeola) is highly contagious; one person infected with measles can infect 9 out of 10 unvaccinated individuals with whom they come in close contact. Most cases reported in 2024 have been among children aged 12 months and older who had not received measles-mumps-rubella (MMR) vaccine. Many countries, including travel destinations such as Austria, the Philippines, Romania, and the United Kingdom, are experiencing measles outbreaks. To prevent measles infection and reduce the risk of community transmission from importation, all U.S. residents traveling internationally, regardless of destination, should be current on their MMR vaccinations. Healthcare providers should ensure children are current on routine immunizations, including MMR. Given currently high population immunity against measles in most U.S. communities, the risk of widescale spread is low. However, pockets of low coverage leave some communities at higher risk for outbreaks.

US: Measles Cases and Outbreaks | CDC   |  GLOBAL: Global Measles Outbreaks (

Clinical Guidance

  • Presentation: Consider measles in patients with fever and rash and ask about recent international travel, exposure to international travelers, or exposure to people with measles. Patients may have non-specific symptoms (fever, cough, coryza, conjunctivitis) without rash in the prodromal phase of infection, so heightened suspicion, particularly during local outbreaks or in patients with recent travel, can be key to timely diagnosis. The incubation period between exposure and initial symptoms is approximately 8-12 days. For images of rash see the Red Book chapter on Measles.
  • Diagnosis:  Measles virus infection can be confirmed by: (1) detection of measles viral RNA by reverse transcriptase-polymerase chain reaction (RT-PCR); (2) detection of measles virus-specific immunoglobulin (Ig) M; (3) a fourfold increase in measles IgG antibody concentration in paired acute and convalescent serum specimens (collected at least 10 days apart); or (4) isolation of measles virus in cell culture.
  • Who is at highest risk of acquiring measles infection:
    • Unvaccinated children or adults
    • Incompletely vaccinated (<2 doses of MMR) children or adults
    • Individuals with known exposure to measles or recent travel to areas with active measles transmission.
  • Who is at highest risk of severe measles infection or complications of measles:
    • Infants and children aged less than 5 years
    • adults aged more than 20 years;
    • pregnant women;
    • people with compromised immune systems, such as from cancer, chemotherapy, or HIV infection
  • Complications: Measles can cause serious illness, even in previously healthy children. Complications of measles can include:
    • Ear infections
    • Diarrhea
    • Pneumonia (either from measles virus itself or from bacterial superinfection)
    • Encephalitis
    • Death
    • In addition, measles infection increases the risk of other severe infections for months or years after measles through the mechanism of immune amnesia.
  • Precautions for patients with suspected or confirmed measles infection: Airborne precautions are needed whenever there is any suspicion of measles exposure. Promptly isolate, collect specimens, and report patients with suspected measles to public health.
  • Prevention of measles: Vaccination is the cornerstone of measles prevention. All children should receive measles vaccination as part of the routine childhood vaccine schedule. Unimmunized or incompletely immunized children should begin catch-up vaccination as soon as possible. During an outbreak, MMR vaccine should be offered to all people with known exposure or in the outbreak community who lack evidence of measles immunity. During a community-wide outbreak that affects infants, MMR vaccine has been shown to be effective in preventing symptoms after exposure and may be recommended for infants 6 through 11 months of age. Children who receive their first MMR vaccine prior to 12 months of age will require two additional doses after 12 months of age for full protection. IGIM administered exposed, measles-susceptible people (not previously vaccinated or immunocompromised) will prevent or attenuate infection if administered within 6 days of exposure.
  • Treatment: There is no specific antiviral agent for treatment of measles infection. Treatment of children with measles with oral vitamin A decreases measles-related morbidity and mortality. Dosing of vitamin A for treatment of children with measles can be found in the Red Book chapter on Measles.
  • Reporting: Involvement of state and local health departments is often advisable for any suspected diagnosis of measles, as there may be specific ways these departments wish to receive specimens and manage patients.
  • For more information see the Red Book chapter on Measles.

Watch this CDC video to learn more about the signs and symptoms of measles to quickly diagnose infected patients. Measles Clinical Features and Diagnosis - YouTube


Pediatric Practice Tools and Info

Watch this CDC video to learn more about the signs and symptoms of measles to quickly diagnose infected patients. Measles Clinical Features and Diagnosis - YouTube

CDC: For Healthcare Professionals - Diagnosing and Treating Measles

CDC: Nearly 40 million children are dangerously susceptible to growing measles threat 

AAP: Communicating with Families and Promoting Vaccine Confidence (

AAP: CDC stresses importance of measles vaccination as cases reported in U.S. | AAP News 


Public Health Resources

CDC: Measles: Information for Public Health Professionals


Infection Prevention and Control Resources

Project Firstline (


Information for Patients and Caregivers

AAP How to Protect Your Children During a Measles Outbreak
In Spanish: Cómo proteger a sus niños durante un brote de sarampión

CDC: Top 4 Things Parents Need to Know about Measles

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