As of May 2025, measles outbreaks have been confirmed in at least 33 jurisdictions of the U.S., with most cases linked to low vaccination rates. The Centers for Disease Control and Prevention (CDC) is urging healthcare providers to talk with travelers about vaccination. Health experts warn that if vaccination rates keep going down, measles could become common again in the U.S., leading to millions of cases over the next 25 years.

While the overall risk is low, measles remains highly contagious. People with advanced heart failure or those who’ve had a heart transplant may have weakened immune systems due to their condition or immunosuppressive treatments. This could make it harder to fight off infections like measles. Although the measles, mumps, rubella (MMR) vaccine is highly effective, immunity can wane over time, which means even previously vaccinated adults may still be at risk.

What Is Measles?

Measles is a very contagious virus. It spreads through the air when someone who is sick coughs, sneezes, or talks, and it can stay in the air for up to two hours after they leave. If you’re exposed to the measles virus and not protected, there’s about a 90 percent chance you’ll get sick.

Symptoms usually begin 10 to 14 days after exposure. Early signs include fever, cough, runny nose, and red, watery eyes. Small white spots may also appear inside the mouth. A few days later, a rash spreads from the face down to the rest of the body. This rash appears red on light skin tones and purple or brown on darker skin tones.

Most people recover in a few weeks, but measles can cause serious complications such as pneumonia, severe diarrhea, and, in rare cases, encephalitis (brain swelling). These risks are higher among babies, older adults, pregnant people, and those with weakened immune systems.

Who’s at Risk for Getting Measles?

People at risk include:

• Those who are unvaccinated or have only had one dose of the MMR vaccine
• Adults who don’t know their vaccination history or were vaccinated before 1968, when less-effective vaccines were used
• Travelers, especially those visiting countries with measles outbreaks or regions in the U.S. where vaccination rates are low
• People living in communities where measles is spreading
• Pregnant individuals, who face a higher risk of complications like preterm birth or fetal loss
• Babies under 1 year old, who are too young to be fully vaccinated
• People in close-contact settings, like schools or shelters, where the virus can spread quickly
• People with weakened immune systems due to health conditions, such as advanced heart failure, or treatments, including heart transplant and immunosuppressive medications

A recent study found that measles could come back and spread more easily across the U.S. if fewer people get vaccinated, especially in areas where many people are not protected.

How Effective Are MMR Vaccines in Preventing Measles?

The measles vaccine is highly effective. After two doses, about 99 percent of people develop lasting immunity. The first dose protects most people, and the second dose helps those who didn’t respond the first time.

Most people remain protected for life. However, rare cases of measles can still occur in vaccinated individuals, especially if their immune system was weak when they got the vaccine, or if their immunity has waned over time.

This is why people living with conditions that may affect the immune system, including certain types of heart disease, should talk to their doctor about whether they need testing or revaccination.

What Are the Risks of Getting an MMR Vaccine?

As with any vaccine, side effects can happen. Common side effects include:

• Mild fever
• Rash
• Temporary swelling of lymph nodes

Some adults may also experience joint pain or minor allergic reactions. Serious side effects are rare.

It’s important to note that multiple studies have found no link between the MMR vaccine and autism.

Talk to your healthcare provider to confirm whether the vaccine is safe and potentially beneficial for you.

Are MMR Vaccines Safe for People With Heart Disease?

Live-virus vaccines like MMR are generally safe for most people with stable heart disease. But if you’re taking immunosuppressive medications — such as after a heart transplant — talk to your doctor first to see what’s right for you. In some cases, a blood test can confirm immunity, and immune globulin (IG) may be recommended as an alternative for short-term protection after exposure.

How Do You Know if You Need an MMR Vaccination or Booster?

Everyone’s health situation is unique. Talk with your doctor to understand your needs. Depending on your history and current health, they may recommend:

• A blood test to check your immunity
• A booster shot if your immunity has faded
• Postponing vaccination and taking additional precautions if your immune system is severely compromised

How Else Can You Protect Yourself and Others From Measles?

The CDC recommends additional precautions:

• Practice good hygiene — Wash hands frequently, avoid touching your face, and clean shared surfaces.
• Be mindful of travel — Before traveling internationally, confirm your vaccine status.
• Limit exposure during outbreaks — Avoid crowded indoor spaces in communities with low vaccination rates.

What Should You Do if You’ve Been Exposed to Measles?

If you’ve been exposed to measles and aren’t vaccinated:

• Getting an MMR vaccine within 72 hours can prevent or reduce illness severity — if you’re eligible.
• If vaccination isn’t safe for you, IG may be given within six days to help protect you.

Check with your doctor to see if you are eligible for any of the above, if you’ve been exposed to measles and aren’t immune.

Stay Protected, Stay Connected

On MyHeartDiseaseTeam, the social network for people with heart disease and their loved ones, people come together to share advice, ask questions, and support one another through challenges like measles outbreaks.

Have you discussed your measles immunity status with your doctor? What steps are you taking to stay protected? Share your experiences and tips in the comments below or start a conversation on your Activities page.