Yes, but it is rare and usually mild

Vaccinated people can get measles, though it happens in roughly 1 to 2 out of every 1,000 people who received two doses of the MMR vaccine. When a vaccinated person does get measles, the illness is almost always milder than in unvaccinated people — fewer spots, lower fever, shorter duration, and almost no serious complications. This is called breakthrough measles.

The MMR vaccine is not a may provide against infection. It is a tool that reduces your risk sharply and protects you from the worst outcomes if infection does occur. Two doses of MMR prevent measles in about 97 to 99 out of 100 vaccinated people. One dose prevents it in about 93 out of 100. Those numbers are high, but not absolute.

Key Takeaways

  • Breakthrough measles in vaccinated people occurs in roughly 1 to 2 per 1,000 people who received two MMR doses, and the illness is usually mild.
  • Vaccinated people who get measles shed the virus for a shorter time and are less contagious than unvaccinated people with measles.
  • Your immunity can fade over decades, which is why some adults born in the 1950s through 1970s have lower protection and may need a booster.
  • If you were vaccinated as a child but unsure of your record, a titer test can measure whether you have protective antibodies.
  • Vaccination still prevents the severe complications of measles — pneumonia, encephalitis, and death — even when breakthrough infection occurs.

Why vaccinated people sometimes get measles

Immunity from the MMR vaccine can fade over time. For most people vaccinated in childhood, protection remains strong for decades. But in some individuals, antibody levels drop enough that the virus can take hold if exposure is heavy or repeated. This is more common in people vaccinated before 1989, when vaccine formulations were different, and in people whose immune systems do not respond as well to vaccines — including those on certain medications or with conditions that affect immunity.

Measles is also highly contagious. A single infected person can spread it to 12 to 18 others in an unvaccinated group. Even vaccinated people in a crowd with sustained exposure may occasionally be overwhelmed by the viral load. This is why outbreaks can include vaccinated individuals, particularly in settings like schools or healthcare facilities where exposure is intense and prolonged.

How breakthrough measles differs from measles in unvaccinated people

Vaccinated people who get measles typically have fewer symptoms and recover faster. The rash is often lighter or slower to appear. Fever is usually lower. Cough and runny nose may be mild or absent. Hospital stays are rare, and serious complications like pneumonia or brain inflammation are uncommon.

Unvaccinated people with measles, by contrast, often have high fevers lasting a week or more, a dense rash covering the entire body, severe cough, and a higher risk of complications. Roughly 1 in 20 unvaccinated children develop pneumonia. About 1 in 1,000 develop encephalitis. Measles kills roughly 1 to 2 out of every 1,000 unvaccinated infected children in developed countries, and far more in places with poor nutrition or limited medical care.

Whether vaccinated people can spread measles to others

Vaccinated people who get breakthrough measles do shed the virus and can transmit it, but they shed for a shorter time and in lower amounts than unvaccinated people. This means they are less contagious overall. A vaccinated person with breakthrough measles is still a risk to unvaccinated people around them — particularly infants too young to be vaccinated and people who cannot receive the vaccine for medical reasons — but the risk is lower than from an unvaccinated case.

This is one reason why high vaccination rates in a community matter even when breakthrough cases occur. If most people are vaccinated, the virus circulates less, spreads more slowly, and has fewer unvaccinated people to infect. Outbreaks in highly vaccinated populations tend to be smaller and shorter than in less vaccinated ones.

Who is at higher risk for breakthrough measles

People vaccinated before 1989 may have lower protection because earlier MMR formulations were less potent. If you were born in the 1950s through 1970s and received one dose as a child, your immunity may have waned. A second dose given later in life can restore protection.

People on immunosuppressive medications — including some treatments for rheumatoid arthritis, Crohn's disease, or cancer — have weaker immune responses to the vaccine and lower protection. People with HIV, particularly those with low CD4 counts, also have reduced vaccine effectiveness. Pregnant people cannot receive the MMR vaccine because it contains live virus, so they rely on immunity from prior vaccination or infection.

People with certain genetic conditions affecting immune function, and those who received the vaccine but whose bodies did not mount an adequate antibody response, are also at higher risk. A blood test called a titer can measure whether your antibodies are at protective levels.

Getting a titer test to check your immunity

If you were vaccinated but have no record, or if you want to know whether your immunity is still strong, your doctor can order a measles titer. This is a blood test that measures the level of antibodies against measles in your system. If the level is protective, you are covered. If it is low, a booster dose of MMR can restore immunity.

Titer testing is particularly useful for healthcare workers, people planning pregnancy, and anyone who will be in close contact with infants or immunocompromised people. Some employers require it. Insurance usually covers the test if your doctor orders it for a medical reason, though coverage varies.

What to do if you think you have been exposed to measles

If you know you were exposed to measles and you are unsure of your vaccination status, contact your doctor or local health department right away. Unvaccinated people can receive the MMR vaccine up to 72 hours after exposure and still prevent or significantly reduce illness. Vaccinated people do not need post-exposure treatment, but your doctor may want to monitor you for symptoms.

Measles symptoms appear 7 to 21 days after exposure, usually around 10 days. Early signs are fever, cough, runny nose, and red eyes — symptoms that look like a cold. A few days later, small white spots appear inside the mouth, followed by a red rash that starts on the face and spreads downward. If you develop these symptoms after known exposure, call your doctor before going in, so they can take precautions to avoid spreading it to others in the waiting room.

Frequently Asked Questions

If I had measles as a child, do I need the vaccine?

No. Infection with measles creates lifelong immunity. If you had measles before the vaccine existed or before you were vaccinated, you are protected for life. Your doctor can order a titer to confirm immunity if you need documentation.

Can the MMR vaccine give you measles?

The MMR vaccine contains live but weakened virus. It cannot cause measles. In rare cases, vaccinated people develop a mild rash a week or two after vaccination, but this is not measles and is not contagious. True measles infection is far more severe.

If I am vaccinated and get measles, will I have permanent immunity after that?

Yes. Infection, even mild breakthrough infection, creates lifelong immunity. You will not get measles again. However, breakthrough measles is uncommon enough that most vaccinated people never experience it.

Should I get a booster if I was vaccinated decades ago?

If you were vaccinated twice as a child or once as an adult, you likely have lasting protection. A booster is usually recommended only if you are at high risk — healthcare worker, planning pregnancy, immunocompromised, or in an area with an active outbreak — or if a titer shows your antibodies are low.

Can a vaccinated pregnant person pass measles immunity to her baby?

Yes. Maternal antibodies pass to the baby during pregnancy and provide some protection in the first few months of life. This is temporary — it fades by 6 to 12 months — but it can reduce severity if the infant is exposed before vaccination begins at 12 months.