Up to 20,000 people who attended a religious gathering may have been exposed to measles. What should they do next?

By Katia Hetter, CNN

Up to 20,000 people who attended a religious gathering at a college in Wilmore, Kentucky, in February could have been exposed to a person later diagnosed with measles.

On Friday, the US Centers for Disease Control and Prevention issued an alert to clinicians and public health officials about the confirmed case of measles in an individual present at the gathering who had not been vaccinated against the disease.

“If you attended the Asbury University gathering on February 17 or 18 and you are unvaccinated or not fully vaccinated against measles, you should quarantine for 21 days after your last exposure and monitor yourself for symptoms of measles so that you do not spread measles to others,” according to the CDC advisory.

The CDC also recommended that people who are unvaccinated receive the measles, mumps, and rubella (MMR) vaccine.

Reading this news, people may have questions about measles, including its symptoms, infection outcomes and who is most at risk. They may also want to know what makes measles so contagious, what has been the cause of recent outbreaks and how effective the MMR vaccine is.

To help answer these questions, I spoke with CNN Medical Analyst Dr. Leana Wen, an emergency physician and professor of health policy and management at the George Washington University Milken Institute School of Public Health. Previously, she served as Baltimore’s health commissioner, where her duties included overseeing the city’s immunization and infectious disease investigations.

CNN: What is measles, and what are the symptoms?

Dr. Leana Wen: Measles is an extremely contagious illness that’s caused by the measles virus. Despite many public health advances, including the development of the MMR vaccine, it remains a major cause of death among children globally.

The measles virus is transmitted via droplets from the nose, mouth or throat of infected individuals. If someone is infected and coughs or sneezes, droplets can land on you and infect you. These droplets can land on surfaces, and if you touch the surface and then touch your nose or mouth, that could infect you, too.

Symptoms usually appear 10 to 12 days after infection. They include a high fever, runny nose, conjunctivitis (pink eye) and small, painless white spots on the inside of the mouth. A few days after these symptoms begin, many individuals develop a characteristic rash — flat red spots that generally start on the face and then spread downward over the neck, trunk, arms, legs and feet. The spots can become joined together as they spread and can be accompanied by a high fever.

CNN: What are outcomes of measles infections? Who is most at risk?

Wen: Many individuals recover without incident. Others, however, can develop severe complications.

One in five unvaccinated people with measles are hospitalized, according to the CDC. As many as 1 out of every 20 children with measles will get pneumonia; about 1 in 1,000 who get measles can develop encephalitis, a swelling of the brain that can lead to seizures and leave the child with lasting disabilities. And nearly 1 to 3 out of every 1,000 children who are infected with measles will die.

Measles is not only a concern for children. It can also cause premature births in pregnant women who contract it. Immunocompromised people, such as cancer patients and those infected with HIV, are also at increased risk.

CNN: What makes measles so contagious?

Wen: Measles is one of the most contagious diseases in the world — up to 90% of the unvaccinated people who come into contact with a contagious individual will also become infected. The measles virus can remain in the air for up to two hours after an infected person leaves an area.

Another reason why measles spreads so easily is its long incubation period. In infected people, the time from exposure to fever is an average of about 10 days, and from exposure to rash onset is about 14 days — but could be up to 21 days. In addition, infected people are contagious from four days before rash starts through four days after. That’s a long period of time where they could unknowingly infect others.

CNN: What has been the cause of recent measles outbreaks?

Wen: It’s important to note that this incident in Kentucky is not yet considered an outbreak. Only one person has been diagnosed with measles. That person was possibly exposed to many others given the number of people in attendance at this gathering, but we don’t know yet if any of those people were infected.

But let’s look at a recent example of a confirmed outbreak in the US: In November 2022, health officials in central Ohio raised alarm over young children being diagnosed with measles. In all, 85 children got sick. None of the children died, but 36 needed to be hospitalized. All those infected were either unvaccinated or not yet fully vaccinated.

Health officials were able to contain the outbreak through contact tracing, vaccination and other public health measures in early February, and it was declared over. But there is concern it won’t be the last of its kind. A study from the CDC reported the rate of immunizations for required vaccines among kindergarten students nationwide dropped from 95% in the 2019-20 school year to 93% in the 2021-22 school year. Some communities have far lower rates than this national average, however, which can lead to outbreaks — not only of measles but also diseases like polio that can also have severe consequences.

CNN: How effective is the MMR vaccine?

Wen: The MMR vaccine is a two-dose vaccine. The recommendation is for children to receive the first dose at age 12-15 months and the second dose at age 4-6 years. One dose of the MMR vaccine 93% effective at preventing measles infection. Two doses are 97% effective.

CNN: What is the best way to protect against measles?

Wen: The MMR vaccine is an extremely safe and very effective vaccine and is recognized as a significant public health advance for preventing an otherwise extremely contagious disease from spreading and causing potentially very severe — even fatal — outcomes.

Consider that the vaccine was licensed in the US in 1963. In the four years before that, there were an average of more than 500,000 cases of measles every year and over 430 measles-associated deaths. By 1998, there were just 89 cases and no measles-associated deaths. That’s a huge public health triumph.

Young children should receive the vaccine according to the recommended schedule. Older kids and adults who never received it should also discuss getting it with their health care provider. And clinicians and public health officials in the US and around the world should redouble efforts to increase routine childhood immunizations so as to stop preventable diseases from making a comeback.

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