The MMR vaccine is given in two doses: the first between 12 and 15 months of age, and the second between 4 and 6 years old

The measles, mumps, and rubella (MMR) vaccine follows a two-dose schedule because one dose does not produce immunity strong enough to last a lifetime in all children. The first dose, given as a single shot, protects about 93 percent of children who receive it. The second dose raises that protection to 97 percent or higher. Both doses are needed to reach the level of immunity that prevents outbreaks in communities.

The timing matters because infants under 12 months still have some protection from antibodies passed from their mother during pregnancy, but that protection fades. By 12 months, most children have lost that maternal immunity and can respond well to the vaccine. The second dose is spaced years apart because immunity from the first dose is already strong by age 4 or 5—the spacing is not about waiting for immunity to wear off, but about ensuring a second exposure that locks in long-term protection.

Key Takeaways

  • The first MMR dose is given between 12 and 15 months; the second is given between 4 and 6 years old, before school entry.
  • Two doses are necessary because the first dose protects about 93 percent of children, while two doses protect 97 percent or more.
  • Infants under 12 months still have some protection from their mother's antibodies, so the vaccine is not given before 12 months in routine schedules.
  • If a child misses the second dose by age 6, it can be given at any later age—there is no need to restart the series.
  • Children who received one dose before age 12 months should receive two additional doses starting at 12 months to count as fully vaccinated.

Why the first dose waits until 12 months

Newborns and infants under 12 months receive antibodies from their mother that provide temporary protection against measles, mumps, and rubella. These maternal antibodies interfere with the vaccine—if you give the MMR vaccine too early, the mother's antibodies will neutralize the vaccine virus before the child's own immune system can learn to recognize it. The vaccine will not work, and the child will not develop immunity.

By 12 months, most children have lost enough of these maternal antibodies that the vaccine can work. This is why 12 months is the standard starting point. In rare situations—such as during a measles outbreak or before international travel—a dose can be given as early as 6 or 9 months, but this early dose does not count toward the two-dose series. The child would still need two additional doses starting at 12 months to be fully protected.

The second dose and school requirements

The second MMR dose is given between 4 and 6 years old, typically before a child enters kindergarten. Most states require proof of two MMR doses before school entry, though the exact age requirement varies by state. Some states allow the second dose to be given as soon as 28 days after the first dose if there is a medical reason to speed up the schedule, but the standard interval is years apart.

If a child reaches school age without the second dose, the school will usually require it before attendance begins. There is no penalty for receiving the second dose late—it works just as well at age 7, 10, or 15 as it does at age 5. The key is that both doses are eventually received.

What happens if the schedule is delayed or missed

If a child misses the first dose at 12 to 15 months, it can be given at any later age. There is no need to wait or restart. Similarly, if the second dose is not given by age 6, it can be given whenever it becomes possible—at age 8, 12, or even in adulthood. The two doses do not have to be given in a specific calendar year or within a certain number of months of each other, as long as both are eventually received.

The only exception is if a child received a dose before 12 months of age (such as during an outbreak). That early dose does not count, and the child needs two additional doses starting at 12 months. A child who received one dose at 10 months and another at 14 months would still need a third dose to be fully protected.

Catch-up vaccination for older children and adults

Children who never received any MMR vaccine can start the series at any age. Two doses, given at least 28 days apart, provide full protection. Teenagers and adults who have no record of vaccination or immunity can also receive the two-dose series. There is no upper age limit—the vaccine works in adults just as it does in children, though adults who were born before 1957 are often considered immune to measles based on the likelihood they had the disease naturally.

Adults born in 1957 or later who have no record of MMR vaccination should receive at least one dose. Healthcare workers, people traveling internationally, and those in close contact with infants should receive two doses regardless of birth year. A blood test can determine whether someone is immune if vaccination records are unavailable.

Why spacing matters less than you might think

The 28-day minimum interval between doses is a safety guideline, not a biological requirement. If the second dose is given fewer than 28 days after the first, it does not provide additional protection and does not count—the child would need a third dose. However, if more time passes between doses, the vaccine works just as well. A child who receives the first dose at 12 months and the second dose at age 8 is just as protected as a child who receives both doses on schedule.

This flexibility matters for families who move, change healthcare providers, or face barriers to keeping appointments. The vaccine series does not reset or expire. A child can receive the first dose, wait years, and then receive the second dose without any loss of effectiveness.

Frequently Asked Questions

Can my baby get the MMR vaccine before 12 months?

In routine circumstances, no—maternal antibodies will prevent the vaccine from working. However, during a measles outbreak or before international travel, a dose can be given as early as 6 months. This early dose does not count toward the required two doses, so your child would still need two additional doses starting at 12 months.

What if my child is allergic to eggs or gelatin?

The MMR vaccine contains gelatin and is grown in eggs. Children with severe allergies to either should discuss vaccination with their doctor. Most children with egg allergies can safely receive the MMR vaccine, and the benefit of protection against measles, mumps, and rubella usually outweighs the risk. A doctor can advise on whether the vaccine is safe for your child.

Do I need to give both doses if my child already had measles, mumps, or rubella?

Having the disease provides lifelong immunity to that specific illness, but the vaccine protects against all three. A child who had measles naturally still needs protection against mumps and rubella. A blood test can confirm immunity to specific diseases if you are unsure whether your child had them.

Is the MMR vaccine safe for children with weakened immune systems?

The MMR vaccine is a live vaccine, meaning it contains a weakened form of the virus. Children with severely weakened immune systems—such as those with untreated HIV or undergoing chemotherapy—should not receive it. Children with mild immune issues or those taking certain medications should discuss the vaccine with their doctor, who can determine whether it is safe or whether an alternative approach is needed.

Can adults who were vaccinated as children still get measles, mumps, or rubella?

Breakthrough infections—where a vaccinated person still gets sick—are rare but possible, especially with measles. Two doses of the MMR vaccine protect 97 percent or more of people. Those who do get sick despite vaccination typically have milder illness than unvaccinated people. Adults unsure of their vaccination history can receive the vaccine again; an extra dose causes no harm.