Babies typically receive their first measles vaccine dose at 12 months old

The first dose of the measles, mumps, and rubella (MMR) vaccine is given at 12 months of age. This timing allows the infant's immune system to respond effectively to the vaccine. A second dose follows at 4 to 6 years old, before school entry, though it can be given as soon as 28 days after the first dose if faster protection is needed.

Infants younger than 12 months are not routinely vaccinated against measles because maternal antibodies—protection passed from the mother during pregnancy—interfere with the vaccine's ability to work. These maternal antibodies fade by around 12 months, making that the earliest age the vaccine becomes effective. Babies born to mothers who were vaccinated or had measles retain some protection during their first year, but this protection is temporary and incomplete.

Key Takeaways

  • The first MMR dose is given at 12 months old; the second dose at 4 to 6 years old.
  • Infants under 12 months have some protection from maternal antibodies, but this fades and is not reliable against measles exposure.
  • If a baby under 12 months is exposed to measles, the MMR vaccine can still be given within 72 hours of exposure to prevent or reduce illness severity.
  • Premature infants are counted from their corrected age (adjusted for prematurity) when determining vaccination timing.
  • Children who miss the routine schedule can receive both doses at any age, with at least 28 days between them.

Why babies under 12 months are not routinely vaccinated

Maternal antibodies are the reason the MMR vaccine is delayed until 12 months. During pregnancy, a mother who was vaccinated or previously had measles passes antibodies to her fetus through the placenta. These antibodies circulate in the newborn's bloodstream and provide some protection against measles during the first months of life.

When a vaccine is given while these maternal antibodies are still present, the antibodies neutralize the vaccine virus before the baby's own immune system can learn to recognize and fight measles. The vaccine does not work as intended. By 12 months, maternal antibodies have declined enough that the vaccine can trigger a strong immune response. The exact timing varies slightly from baby to baby, but 12 months is the age when most infants have lost enough maternal protection for the vaccine to be effective.

What happens if a baby under 12 months is exposed to measles

If an infant under 12 months has direct contact with someone who has measles, the MMR vaccine can be given as early as possible after exposure—ideally within 72 hours. This is called post-exposure vaccination. The vaccine may prevent measles from developing or reduce how severe the illness becomes, though protection is not may provide at this age.

Some infants exposed to measles may also receive an injection of measles immunoglobulin (a concentrated antibody preparation) within 6 days of exposure. This provides temporary passive protection while the baby's immune system develops its own response. A pediatrician or public health department can advise on whether this additional protection is needed based on the exposure circumstances and the baby's age.

The second dose and catch-up schedules

The second MMR dose is given at 4 to 6 years old, typically before school entry. This second dose catches the small percentage of children whose immune systems did not respond fully to the first dose. It also provides a booster for those whose immunity has waned slightly over time.

If a child misses either dose on schedule, they can receive both doses at any later age, as long as there are at least 28 days between them. A child who received their first dose at age 2, for example, can receive their second dose 28 days later rather than waiting until age 4 to 6. Catch-up vaccination is important because measles spreads quickly in unvaccinated populations, and each additional vaccinated person in a community reduces the risk for infants too young to be vaccinated.

Premature infants and adjusted age

Premature infants follow a modified vaccination schedule based on their corrected age (also called adjusted age), not their age since birth. Corrected age is calculated by subtracting the number of weeks the baby was born early from their current age. For example, a baby born 8 weeks early would receive the MMR vaccine at 12 months corrected age, which is about 14 months after birth.

This adjustment accounts for the fact that premature infants' immune systems develop on a timeline closer to their due date than their birth date. Using corrected age ensures the vaccine is given when the infant's immune system is genuinely ready to respond, rather than giving it too early and having it fail due to residual maternal antibodies or immune immaturity.

Reasons a baby might receive MMR earlier than 12 months

In certain situations, the first MMR dose can be given as early as 6 to 11 months old, though this is not routine. These situations include travel to areas where measles is circulating, outbreak response, or post-exposure vaccination. When MMR is given before 12 months, a repeat dose is needed at 12 months or later, followed by a second dose at least 28 days after that.

A baby traveling internationally to a country with measles cases may receive an early dose before departure to provide some protection during travel. After returning home, the routine two-dose schedule is still followed. Similarly, during a measles outbreak in a community, public health officials may recommend early vaccination for infants in affected areas to slow transmission.

Frequently Asked Questions

Can I give my baby the MMR vaccine before 12 months if I'm worried about measles?

Routine vaccination before 12 months is not recommended because maternal antibodies prevent the vaccine from working. However, if your baby has been exposed to measles or will travel to an area with measles cases, contact your pediatrician about early vaccination. Early doses require additional doses later to ensure full protection.

What if my baby was born prematurely—when should they get the vaccine?

Use your baby's corrected age (adjusted for prematurity) to determine vaccination timing. A baby born 10 weeks early receives MMR at 12 months corrected age, which is about 14 months after birth. Your pediatrician will calculate corrected age at each visit.

Does my baby need the MMR vaccine if I had measles?

Yes. Your baby received some protection from your antibodies during pregnancy and early infancy, but this protection fades and is incomplete. The MMR vaccine at 12 months provides lasting immunity. If you are unsure whether you had measles or were vaccinated, your doctor can check your immunity status.

What if we missed the 12-month appointment—is it too late?

No. Your child can receive the first MMR dose at any age after 12 months. The second dose should follow at least 28 days later. Contact your pediatrician to schedule both doses. Catch-up vaccination is important because unvaccinated children can contract measles and spread it to infants too young to be vaccinated.

Are there any babies who should not receive the MMR vaccine?

Most babies can safely receive MMR at 12 months. Exceptions are rare and include babies with severe allergies to vaccine components or certain immune system conditions. Your pediatrician will review your baby's health history before vaccination and discuss any concerns specific to your child.