As the measles outbreak continues to spread in the U.S., Jan K. Carney, M.D., MPH, associate dean for public health & health policy at the Larner College of Medicine and Patsy Tassler Kelso, Ph.D., state epidemiologist of infectious disease with the Vermont Department of Health, discussed the realities of the measles outbreak and what it means to Vermonters.

In the United States, measles cases have increased by a whopping 360%, with nearly 500 cases across 21 states, including Vermont, mainly affecting unvaccinated individuals. Two unvaccinated children have died from measles since February. Public health officials warn that low immunization rates, increased travel, and community transmission could drive further outbreaks.

How does an outbreak occur after measles was considered eradicated in the United States in 2000?

Measles was declared eliminated in the United States in 2000. This was due to a very high percentage of people receiving the safe and effective measles, mumps, and rubella (MMR) vaccine. Measles is still a common disease in many parts of the world, including Europe, the Middle East, Asia, and Africa. Measles is highly contagious, and every year, measles is brought into the U.S. by unvaccinated travelers who contract measles while they are in other countries. The risk of widespread measles outbreaks in the U.S. is low because most people in the U.S., including Vermont, are vaccinated against measles. However, there are still communities across the nation with lower vaccine coverage and therefore higher risk for outbreaks. So far in 2025, there are ongoing outbreaks in Texas, New Mexico, and also Quebec, Canada. 

Compared to other diseases, how contagious is measles? 

Measles is one of the most contagious diseases. The measles virus lives in an infected person's nose and throat mucus. The virus can spread to other people when an infected person coughs or sneezes. Other people can become infected if they breathe the contaminated air or touch a surface with the virus, then touch their eyes, noses, or mouths. An infected person can spread measles to others even before knowing they have the disease—from four days before developing the measles rash through four days afterward. The virus can stay in the air for up to two hours after an infected person leaves an area. An infected person will spread measles to about 90% of people they come into contact with who are not vaccinated. 

What are the symptoms and complications of measles? Who is most at risk?

Symptoms usually start with a high fever, then a cough, runny nose, and red and watery eyes. A rash usually appears three to five days after the first symptoms. Some people may suffer from severe complications, such as pneumonia (infection of the lungs) and encephalitis (swelling of the brain). They may need to be hospitalized and could die. Measles can also lead to long-term complications that develop 7 to 10 years after a person has measles. Babies, young children, and people with weak immune systems are at higher risk of getting very sick from measles. 

Can measles affect adults?

Yes. Of the 607 confirmed cases in the U.S. to date in 2025:

196 (32%) are under 5 years of age
240 (40%) are 5-19 years of age
159 (26%) are 20+ years of age 
12 (2%) have no age reported

How effective is the measles vaccine?

Measles is almost entirely preventable with vaccines. Measles vaccines are safe and highly effective.  Two vaccine doses are 97% effective against measles, and one dose is 93% effective. 

Is there a booster shot for measles? If so, who should get a booster?

If you were born before 1957, you are likely protected against measles. 

If you were born in 1957 or later: 

• You are protected from measles if you have received either 1 or 2 doses of MMR or MMRV vaccine.
• Some people do need 2 doses of MMR or MMRV: students at post-high school education institutions, health care personnel, international travelers, close contacts of immunocompromised people, and people with HIV infection. 

If you were vaccinated in the 1960s: 

• An inactivated measles vaccine was used from 1963 to 1967. This vaccine was found to be not effective. If you were vaccinated before 1968 with either an inactivated measles vaccine, or measles vaccine of unknown type, you should receive at least one dose of the MMR vaccine. You should receive two if you have the risk factors listed above. 

If you aren’t sure and have your doctor says it’s okay, you can get a measles vaccination. There is no harm in giving the MMR vaccine to someone who may already be immune.  

What should you do if you suspect you or a loved one has measles?

If you think you or a family member might have measles, contact your doctor right away. Make sure to call before going to a doctor’s office, the hospital, or a clinic to let them know about symptoms. Because the virus is so contagious, the office will need to take precautions before you arrive. Stay at home and away from other people as much as possible to limit the risk of getting other people sick. 

Is it safe to travel during a measles outbreak?

Yes, but make sure your family is vaccinated against measles – especially children and people with weakened immune systems. It’s particularly important if you plan to travel outside of the U.S. Review your and your family’s vaccination records or talk to your doctor to make sure you are protected against measles. 

I’m traveling to another country. What should I do to prepare?

Before you travel, tell your doctor where you are traveling. Babies and children may need measles vaccination at a younger age than usual. After you travel, if anyone gets a fever and rash within three weeks of returning from your trip, call your doctor. 

For more information on making sure you and your family are protected before traveling internationally, visit Plan for Travel - Measles (CDC).

When there is a measles case, the health department role includes these activities:

• Identify and notify people who came into contact with a person infected with measles.
• Determine whether people who were exposed to measles have evidence of immunity.
• Provide post-exposure vaccines, including a second dose, if appropriate.
• Recommend and provide post-exposure immune globulin (IG) for people who are at higher risk of getting seriously ill from measles.
• Monitor the symptoms of people who have had close contact with a case of measles and provide recommendations to limit risk to communities.
• Recommend self-isolation and monitoring for measles signs and symptoms in susceptible contacts as needed.
• Communicate with partner agencies, health care providers, and the public.