Measles Outbreak Management in California
Vaccination Schedule
All children should receive two doses of MMR vaccine: the first at 12-15 months and the second at 4-6 years before school entry. 1, 2
Routine Childhood Vaccination
- Preschool children (12 months to kindergarten): One dose of MMR administered on or after the first birthday 1
- School-age children (kindergarten through grade 12): Two doses of MMR separated by at least 28 days, with the first dose given no earlier than the first birthday 1
- Doses given before the first birthday do not count toward adequate vaccination 1
High-Risk Groups Requiring Two Doses
- Healthcare workers born during or after 1957: Two doses of MMR separated by at least 28 days 1
- College students and post-high school educational institution attendees: Two doses 2, 3
- International travelers: Two doses administered at least 28 days apart 1, 2
- Adults at increased risk for exposure: Two doses 2
Special Considerations for Healthcare Workers
Healthcare facilities should consider vaccinating even workers born before 1957 who lack documented immunity, as 27% of measles cases among healthcare workers during 1985-1992 occurred in persons born before 1957. 1
Outbreak-Specific Vaccination Requirements
During measles outbreaks, all school-aged children, adolescents, and adults born during or after 1957 who are at risk for exposure must have two doses of measles-containing vaccine separated by at least 28 days. 1
Outbreak Vaccination Protocols
- Preschool-aged children (≥12 months): Authorities should extend the two-dose requirement to all children aged ≥12 months during outbreaks involving preschool-aged children 1
- Serologic screening before vaccination is NOT recommended during outbreaks because rapid vaccination is necessary to halt disease transmission 1
- No minimum interval is required for the second dose if the first dose was given more than 28 days ago 2
Post-Exposure Prophylaxis (PEP)
MMR Vaccine as PEP
- MMR vaccine should be administered within 72 hours of measles exposure to susceptible persons aged ≥12 months without contraindications 3
- Delayed diagnosis and delayed notification of health officials precludes effective use of MMR vaccine as outbreak intervention, as demonstrated in the 2011 Los Angeles refugee-associated outbreak 4
Immune Globulin (IG) for PEP
Immune globulin should be used for post-exposure prophylaxis in persons who cannot receive MMR vaccine or were exposed more than 72 hours ago. 3
IGIM (Intramuscular Immune Globulin) Indications:
- Infants aged birth to 6 months exposed to measles 3
- Immunocompetent persons: Increased recommended dose per 2013 ACIP revisions 3
IGIV (Intravenous Immune Globulin) Indications:
- Severely immunocompromised persons without evidence of measles immunity who are exposed 3
- Pregnant women without evidence of measles immunity who are exposed 3
Evidence of Immunity
Acceptable Evidence (General Population)
Persons can be presumed immune to measles if they have: documentation of adequate vaccination, laboratory evidence of immunity, laboratory confirmation of disease, or were born before 1957. 1, 5, 3
Important 2013 ACIP Revision
Documentation of physician-diagnosed disease is NO LONGER acceptable evidence of immunity for measles and mumps; laboratory confirmation of disease is now required. 3
Laboratory Testing
- Measles-specific IgG antibody detectable by any serologic test (EIA/ELISA preferred over older HI test) indicates immunity 1, 5
- Equivocal serologic test results should be considered negative/susceptible 5
- IgG antibodies should be measured, not IgM (which indicates recent infection) 5
- Post-vaccination serologic testing to verify immune response is NOT recommended 1
Clinical Management
Immediate Actions for Suspected Cases
Clinicians must immediately isolate persons with suspected measles and promptly report them to health authorities. 4, 6
- All suspected measles cases should be confirmed by laboratory testing 1
- Rapid reporting is critical as delayed notification precludes effective outbreak control 4
Case Characteristics and Complications
- Among 704 cases in early 2019,71% were unvaccinated, 9% were hospitalized 6
- In the 2025 multistate outbreak, 96% of 800 patients were unvaccinated or had unknown vaccination status, 11% were hospitalized, and three died 7
- Complications include pneumonia, encephalitis, and death 6
Public Health Actions
Outbreak Investigation and Response
The 2011 Los Angeles outbreak required 50 staff members to interview 298 contacts, demonstrating the resource-intensive nature of measles outbreak response. 4
Community-Level Interventions
- Public health departments should work with trusted community messengers on culturally competent community engagement and education 7
- Coordinate with health care facilities and schools for vaccination efforts 7
- Implement community infection prevention approaches including case isolation, contact monitoring, and post-exposure prophylaxis 7
High-Risk Communities
Six of 13 outbreaks in 2019 were associated with underimmunized close-knit communities and accounted for 88% of all cases. 6
- The 2025 multistate outbreak predominantly affected close-knit communities with low vaccination coverage in New Mexico, Oklahoma, and Texas, accounting for 82% of 800 total cases 7
- Targeted vaccination efforts in these communities are essential 6, 7
International Travel Considerations
Pre-Travel Vaccination
Children aged ≥12 months traveling internationally should receive two doses of MMR separated by at least 28 days before departure, with the first dose on or after the first birthday. 1
- Infants aged 6-11 months should receive monovalent measles vaccine before departure (or MMR if monovalent unavailable) 1
- Children vaccinated before 12 months should be revaccinated with two doses of MMR: first at 12-15 months (or 12 months if remaining in high-risk area) and second at least 28 days later 1
Travel-Associated Cases
Among 48 internationally imported cases in 2025,92% occurred among U.S. residents, highlighting the importance of pre-travel vaccination. 7
- Increased global measles activity poses ongoing risk to U.S. elimination, particularly when unvaccinated travelers acquire measles abroad and return to communities with low vaccination rates 6
Special Populations
HIV-Infected Persons
All persons aged ≥12 months with HIV infection who do not have current severe immunosuppression should be vaccinated with MMR. 3
- Persons with perinatal HIV infection vaccinated before effective ART should be revaccinated with two appropriately spaced doses once effective ART is established 3
- Recommended timing: 12-15 months and 4-6 years 3
Healthcare Personnel
All healthcare workers (medical or nonmedical, paid or volunteer, with or without patient-care responsibilities) must be immune to measles. 1
- Serologic screening before vaccination is not necessary unless cost-effective, and only if identified susceptible persons will be vaccinated promptly 1
- During outbreaks, serologic screening is not recommended 1
Common Pitfalls
- Do not count doses given before the first birthday toward adequate vaccination 1
- Do not delay vaccination for serologic testing during outbreaks 1
- Do not accept physician-diagnosed disease as evidence of immunity without laboratory confirmation 3
- Do not assume birth before 1957 guarantees immunity in healthcare workers or during outbreaks 1
- Do not wait for documentation when rapid vaccination is needed—there is no harm in vaccinating someone who may already be immune 2