As of April 2025, measles outbreaks have been confirmed in 25 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.

While the overall risk is low, measles remains highly contagious. People living with HIV may be more vulnerable if their immune system is weakened — particularly those with low CD4 counts. And 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 Are 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, including some people living with HIV.

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 living with HIV, if their immune system is weak

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 HIV or other conditions that affect the immune system 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. Also, 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 necessary for you.

Are MMR Vaccines Safe for People With HIV?

The MMR vaccine is considered safe for most people living with HIV — especially those who are not severely immunocompromised. If your CD4 count is above 200 cells per cubic millimeter or your CD4 percentage is at least 15 percent, you can receive the vaccine in two doses, 28 days apart. While the immune response may be weaker than in the general population, the vaccine still offers important protection. Measles can be especially dangerous for people with HIV, making prevention critical.

Reputable health agencies and organizations — including the U.S. Department of Health and Human Services’ HIV.gov, the World Health Organization (WHO), and Aidsmap — support the safety and effectiveness of the MMR vaccine for adults and children over 12 months living with HIV, as long as they aren’t severely immunocompromised.

How Can You Tell 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 you’re not eligible for vaccination (e.g., immunocompromised or pregnant), immune globulin (IG) within six days can offer protection.

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 myHIVteam — the social network for people with HIV and their loved ones, more than 43,000 people with HIV come together to ask questions, give advice, and share their stories.

Have you talked to your doctor about your measles immunity or vaccination status? How do you stay informed and prepared during outbreaks like this? Share your experiences in the comments below, or start a conversation by posting on your Activities page.