With outbreaks of measles occurring across the country, the largest in Texas with 279 cases including 36 hospitalizations and one death as of March 18, 2025, measles is on everyone’s minds. The first article in this series described clinical suspicion of measles and how to make a measles diagnosis. In Part 2 we discuss who should receive a measles vaccine, both in the routine vaccination schedule and in outbreak settings.
Routine Measles Vaccination Schedule:
In the U.S., the measles vaccine comes in two versions: MMR (protecting against measles, mumps, and rubella) and MMRV (MMR plus varicella [AKA chickenpox]). Both vaccines consist of a two-dose series with the first dose recommended at 12-15 months of age and the second dose between the ages of four and six years. Most often, the first dose is given at the one-year childhood well visit and the second dose at a well visit before the child starts kindergarten.
Catch-up Measles Vaccination Schedule:
For any unvaccinated person over one year old who did not receive the routine schedule, a two-dose series should be initiated as soon as possible. If MMR is given as the first dose, either MMR or MMRV can be given after 28 days. If MMRV is used as the first dose, the second dose of MMRV can be given at least three months later. In both cases, if the child is younger than four years old, they can get their second dose based on the routine schedule (at four-to-six years of age).
Other People Who Should Consider Measles Vaccination:
There are a few other situations in which someone might consider measles vaccination.
In general, adults without evidence of immunity should get at least one dose of MMR. Evidence of immunity consists of documentation of adequate vaccination, laboratory evidence of immunity, birth before 1957 (because everyone got measles back then), or laboratory confirmation of measles infection.
Some international travelers should consider MMR vaccination. Infants aged six-to-eleven months should receive a dose of MMR prior to travel (followed by the normal age-appropriate series). Children at least one year old, adolescents, and adults without evidence of immunity should get two doses of MMR vaccine separated by at least 28 days prior to travel.
Healthcare personnel, college students, and persons with childbearing potential should ensure immunity before starting work, school, or becoming pregnant. Catch-up vaccination is recommended for anyone without evidence of immunity.
Another group of individuals who may consider having an additional MMR vaccination are those who were vaccinated with either an inactivated measles vaccine or a vaccine of unknown type between 1957 and 1968. The inactivated measles vaccine was not effective, and it is recommended that these individuals be revaccinated with at least one dose of MMR.
Accelerated Measles Vaccination Schedule in an Outbreak Setting:
Children as young as six months old can be safely vaccinated with the MMR vaccine, and in an outbreak setting, families (in consultation with their child’s pediatrician) may consider vaccinating earlier than the typical 12-15 month range to provide protection for at-risk infants. While the immune response generated by a six-month-old is generally weaker than that of a one-year-old, some protection from early vaccination is better than none in an outbreak setting. Babies who get an early vaccination should then receive the age-appropriate two-dose series.
The second dose of MMR/V can also be given earlier during a measles outbreak as long as it’s more than 28 days after the first dose. One dose confers approximately 93 percent protection, while two doses raises this up to about 97 percent protection. Children between one and three years old don’t have to wait until age four to receive their second dose if they reside in an outbreak area.
Additionally, adolescents and adults without evidence of immunity in an outbreak setting should consider two doses of MMR separated by at least 28 days.
For unvaccinated persons with possible exposure to measles (i.e. postexposure prophylaxis), one dose of MMR should be administered within 72 hours of exposure and the second dose delivered at least 28 days later.
Vaccination is the best way to prevent measles because the virus is so highly contagious. Models estimate that about 95 percent immunity in a population is necessary to keep measles at bay. Since there are many people who are unable to be vaccinated (including babies under six months of age and persons with a contraindication to vaccination) as well as people who remain vulnerable even after vaccination (such as persons with immunocompromise), it’s important that everyone who can be vaccinated receive the vaccine.
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Stay tuned for the next article in this series Measles Outbreaks in the United States: Complications of Measles and subscribe below to get the next article delivered to your inbox.
