Yes, but it is very rare

You can get measles after vaccination, but the risk is small. The measles vaccine is about 97 percent effective after two doses. That means roughly 3 out of every 100 vaccinated people could still catch measles if exposed to the virus. A single dose is about 93 percent effective, which is why two doses are recommended.

When vaccinated people do get measles, the illness is usually milder than in unvaccinated people. They tend to have fewer spots, lower fevers, and shorter illness duration. Serious complications like pneumonia or brain inflammation are much less common in vaccinated people who break through with measles.

Key Takeaways

  • The measles vaccine is about 97 percent effective with two doses, meaning a small percentage of vaccinated people can still get measles if exposed.
  • Breakthrough measles in vaccinated people is usually milder, with fewer symptoms and lower risk of serious complications.
  • Your immune response to the vaccine weakens over time, but two doses provide long-lasting protection for most people.
  • Outbreaks are more likely to spread in communities with lower vaccination rates, which increases exposure risk for everyone.
  • If you are vaccinated and exposed to measles, you should still contact a doctor because antiviral treatment may reduce illness severity.

Why vaccination does not may provide immunity

No vaccine is 100 percent effective. The measles vaccine works by training your immune system to recognize and fight the virus, but the strength of that training varies from person to person. Some people's immune systems respond very strongly to the vaccine and build robust protection. Others mount a weaker response, leaving them vulnerable if they encounter the actual virus.

Age at vaccination matters. Children vaccinated before 12 months old have lower response rates than those vaccinated at 12 to 15 months, which is the standard age for the first dose. Certain medical conditions and medications that suppress the immune system can also reduce how well the vaccine works. People with HIV, those undergoing chemotherapy, or those taking immunosuppressive drugs for autoimmune conditions may not develop full protection even after vaccination.

How your immunity changes over time

Your antibody levels—the proteins your immune system makes to fight measles—naturally decline after vaccination. This happens with most vaccines. However, your immune system also develops memory cells that can quickly recognize measles if you encounter it years or decades later. These memory cells usually prevent infection entirely, but occasionally they respond slowly enough that the virus establishes itself before being cleared.

The two-dose schedule exists partly to address this. The first dose primes your immune system. The second dose, given at least 28 days later, boosts antibody levels and strengthens memory cell formation. Two doses provide much more durable protection than one dose alone. Studies show that protection from two doses remains very high even 30 to 40 years after vaccination.

What happens when vaccinated people get measles

Breakthrough measles—measles in a vaccinated person—typically looks different from measles in unvaccinated people. Vaccinated people often have fewer of the characteristic red spots, and the spots may not follow the typical pattern of spreading from face to trunk to limbs. Fevers are usually lower, and the illness resolves faster, often within a few days rather than a week or more.

The rash may be atypical enough that doctors initially miss the diagnosis. Some vaccinated people develop only a few spots or a faint rash. Others have respiratory symptoms like cough without much of a rash at all. This atypical presentation is actually a sign that vaccination is working—your immune system is controlling the virus before it can cause severe disease.

Breakthrough cases and community spread

Breakthrough measles is more likely to occur during large outbreaks when many people are infected and the virus circulates widely. In communities where most people are vaccinated, measles spreads slowly because it cannot find enough unvaccinated people to infect. In communities with lower vaccination rates, the virus spreads rapidly, and even vaccinated people face higher exposure risk.

Vaccinated people who do get measles can still transmit it to others, though they are generally less contagious than unvaccinated people. They shed virus for a shorter period and usually have milder symptoms, which means less coughing and sneezing. The main protection for vaccinated people comes not from being in a low-transmission environment, but from the vaccine itself reducing the chance that exposure leads to infection.

Who is at higher risk for breakthrough measles

People vaccinated before 1989 may have received older vaccine formulations or only one dose, depending on their age and the recommendations at the time. Adults born between 1957 and 1989 who received only one dose have a higher breakthrough risk than those who received two doses. Healthcare workers and people who travel internationally face higher exposure risk simply because they encounter more people.

Immunocompromised people—those with HIV, cancer, or taking immunosuppressive medications—have the highest breakthrough risk. They may not have mounted a strong response to the vaccine in the first place, and their weakened immune system cannot respond quickly to exposure. Pregnant people cannot receive the live measles vaccine, so they rely entirely on prior vaccination or natural immunity.

What to do if you are vaccinated and exposed to measles

Contact a doctor if you know you have been exposed to measles, even if you are vaccinated. A doctor can assess your vaccination history and determine your risk. If you develop symptoms like fever, cough, runny nose, or a rash within 7 to 21 days of exposure, report this to your doctor immediately. Measles can be confirmed with a blood test or a swab from the throat or nose.

Antiviral medication called ribavirin may reduce illness severity if given early, particularly for people at high risk of complications. You should also isolate from others while contagious, even if your illness is mild. Vaccinated people with measles are typically contagious from 4 days before the rash appears until 4 days after it appears. Unvaccinated people remain contagious longer.

Frequently Asked Questions

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

Natural measles infection provides lifelong immunity in almost all cases. If you had measles, you do not need vaccination. However, if you are unsure whether you had measles or just assumed you did, a blood test can check for immunity. Many people born before 1957 are considered immune by default because measles was so common.

Can the vaccine give me measles?

The measles vaccine used in the United States (MMR) contains a weakened live virus that cannot cause measles disease. It can cause a mild rash in a small percentage of vaccinated people about 7 to 10 days after vaccination, but this is not measles—it is a vaccine reaction. The rash is not contagious and resolves on its own.

Should I get revaccinated if I am worried about breakthrough risk?

A third dose of measles vaccine is not routinely recommended for people who received two doses, because the benefit is small and immunity from two doses is already very high. However, people in high-risk settings like healthcare workers or those traveling to areas with measles outbreaks may discuss a booster with their doctor. A blood test can also check your antibody level if you want to know your protection status.

What is the difference between breakthrough measles and regular measles?

Breakthrough measles is usually milder, with fewer spots, lower fever, and shorter duration. The rash may be atypical or faint. Unvaccinated measles is more severe, with higher fever, more extensive rash, and higher risk of complications like pneumonia, encephalitis, or death. Vaccinated people are far less likely to need hospitalization.

If measles is so rare now, why do I still need the vaccine?

Measles is rare in the United States because vaccination rates are high, not because the virus disappeared. The virus still circulates in other countries and can be brought in by travelers. If vaccination rates drop, measles outbreaks return quickly. Maintaining high vaccination rates keeps measles rare and prevents the large outbreaks that occur in under-vaccinated communities.