Yes, but it is rare and usually mild

You can get measles even if you have been vaccinated, though the risk is very low. The MMR vaccine (measles, mumps, rubella) prevents measles in about 97 percent of people who receive both doses. The remaining 3 percent can still contract the virus, but their illness is typically much milder than in unvaccinated people—fewer complications, shorter duration, and lower fever.

This does not mean the vaccine failed. Vaccines work by training your immune system to recognize and fight a virus quickly. A vaccinated person who gets measles usually has a weaker infection because their body knows how to respond. An unvaccinated person has no defense and faces a much higher risk of serious complications like pneumonia, encephalitis (brain inflammation), and death.

The medical term for getting a disease despite vaccination is breakthrough infection. Measles breakthrough infections happen, but they are uncommon enough that public health officials consider the vaccine highly effective at the population level.

Key Takeaways

  • The MMR vaccine prevents measles in approximately 97 percent of vaccinated people, meaning about 3 percent can still get infected.
  • Vaccinated people who get measles typically have milder symptoms, fewer complications, and recover faster than unvaccinated people.
  • Breakthrough measles infections are most likely in people who received only one dose instead of the recommended two doses.
  • Your immunity to measles can weaken over decades, though serious breakthrough infections remain uncommon even in older adults.
  • If you are unsure whether you were vaccinated or received both doses, a blood test can measure your measles antibodies.

Why some vaccinated people still get measles

The MMR vaccine is not 100 percent effective because no vaccine is. Some people's immune systems do not respond strongly to the vaccine, or they do not respond at all. This can happen for several reasons: the person may have received the vaccine while their immune system was weakened by another illness, they may have a genetic variation that affects how their body processes vaccines, or they may simply be among the small percentage for whom the vaccine does not trigger a protective response.

The most common reason for breakthrough measles is incomplete vaccination. One dose of MMR provides about 93 percent protection. The second dose, given at least 28 days after the first, brings protection up to 97 percent. People who received only one dose are more vulnerable, and people who never received any doses face the highest risk.

Age also matters. Immunity from the MMR vaccine can gradually decline over several decades, though serious breakthrough infections remain uncommon. A person vaccinated as a child may have lower antibody levels by age 50 or 60, but their immune system still remembers how to fight measles quickly if exposed.

What breakthrough measles looks like

Breakthrough measles typically causes a milder illness than measles in unvaccinated people. Symptoms may include fever, cough, runny nose, and a rash, but the fever is usually lower, the rash may be less extensive, and the illness resolves faster—often within a few days instead of one to two weeks.

Vaccinated people are far less likely to develop the serious complications that make measles dangerous: pneumonia, encephalitis, or secondary infections. They are also less likely to spread the virus to others, though they can still transmit it during the contagious period.

The rash of breakthrough measles may look different from typical measles. It can be less dense, appear in different patterns, or fade more quickly. This variation is one reason measles can be harder to diagnose in vaccinated people—doctors may not immediately recognize it as measles because it does not match the textbook presentation.

How to know if you are protected

If you received two doses of MMR vaccine at least 28 days apart, you are considered protected against measles. The CDC and most state health departments accept this as proof of immunity. You do not need a blood test unless you are unsure whether you were vaccinated or how many doses you received.

If you are uncertain about your vaccination history, you have two options. First, check with your parents, school records, or previous healthcare providers—many keep vaccination records for decades. Second, ask your doctor for a measles antibody test (also called a titer test). This blood test measures whether you have antibodies against measles and can confirm immunity even if you do not have documentation of vaccination.

Some people—including healthcare workers, people traveling internationally, and those born in certain years—may be asked to prove immunity with either vaccination records or an antibody test. If you cannot produce either, your doctor can revaccinate you. A revaccination does not harm you even if you are already immune.

Who is at highest risk for breakthrough measles

People who received only one dose of MMR are at higher risk than those who received two doses. People vaccinated before 1989 (when the two-dose schedule became standard) may have received only one dose and should verify their vaccination history.

People with weakened immune systems—including those with HIV, those taking immunosuppressive medications, or those undergoing cancer treatment—may have a lower response to the vaccine and could be at higher risk for breakthrough infection. If you fall into this category, talk with your doctor about your specific risk.

Older adults vaccinated decades ago may have declining antibody levels, though breakthrough measles remains uncommon in this group. People who travel to countries where measles is still circulating face higher exposure risk and should verify their vaccination status before traveling.

What to do if you think you have measles

If you have fever, cough, runny nose, and a spreading rash, contact your doctor by phone before going to an office or clinic. Tell them you may have measles so they can take precautions to prevent spread to other patients. Do not walk into an urgent care or emergency room without calling first.

Your doctor can diagnose measles through a throat swab, saliva test, or blood test. There is no specific treatment for measles itself—care focuses on managing fever and other symptoms while your immune system fights the infection. Rest, fluids, and fever-reducing medication are the main treatments.

Measles is contagious from about four days before the rash appears until four days after it appears. If you have measles, stay home during this period to avoid spreading it to others, especially to people who are unvaccinated, very young, pregnant, or immunocompromised.

Vaccination still matters even with breakthrough risk

The fact that breakthrough measles can occur does not make the vaccine less valuable. Vaccination dramatically reduces your risk of getting measles at all, and if you do get infected, it ensures your illness will be far milder and less likely to cause serious harm.

From a public health perspective, high vaccination rates protect people who cannot be vaccinated—infants too young for the vaccine, people with severe allergies to vaccine components, and people with certain medical conditions. When enough people are vaccinated, measles cannot spread easily through a population, and outbreaks are prevented.

The alternative to vaccination is not zero risk—it is the risk of unvaccinated measles, which carries a much higher chance of hospitalization, complications, and death. Breakthrough measles is the rare exception; unvaccinated measles is the common outcome when people are not protected.

Frequently Asked Questions

If I was vaccinated as a child, do I need a booster as an adult?

Most adults who received two doses of MMR do not need a booster. Immunity from two doses is considered lifelong for most people. However, if you are traveling internationally, work in healthcare, or have only one documented dose, your doctor may recommend a second dose or a booster.

Can a vaccinated person spread measles to an unvaccinated person?

Yes, though it is less likely than spread from an unvaccinated person. A vaccinated person with breakthrough measles can transmit the virus during the contagious period, but they shed less virus and are contagious for a shorter time. This is one reason vaccination protects communities—it reduces both infection rates and transmission.

What if I had measles before I was vaccinated?

Natural infection from measles provides lifelong immunity. You do not need the vaccine if you have documented measles infection. However, if you are unsure whether you had measles or just think you did, an antibody test can confirm immunity, and vaccination is safe even if you are already immune.

Does the vaccine protect against all types of measles?

There is only one measles virus, though it has different genetic strains circulating in different parts of the world. The MMR vaccine protects against all of them. Breakthrough infections can occur with any strain, but protection remains high across all variants.

If I have a breakthrough infection, will I be immune afterward?

Yes. Natural infection combined with prior vaccination creates very strong, likely lifelong immunity. Your immune system has now seen the real virus and knows how to fight it, in addition to the training it received from the vaccine.