What is measles and what makes it so contagious? Our medical analyst explains

CNN
—

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

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

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

The CDC has also recommended that unvaccinated people get 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 caused recent outbreaks, and how effective the MMR vaccine is.

To help answer these questions, I spoke with Dr. Leana Wen, CNN medical analyst, emergency physician and professor of health policy and management at 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 AS Leana Wen: Measles is a highly contagious disease caused by the measles virus. Despite many advances in public health, including the development of the MMR vaccine, it remains a leading cause of death in children worldwide.

The measles virus is transmitted by droplets from the nose, mouth or throat of infected people. 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, it could also infect you.

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

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

Magnifying glass: Many people recover uneventfully. Others, however, can develop serious complications.

One out of five unvaccinated people with measles are hospitalized, According to the CDC. Up to 1 in 20 children with measles will develop pneumonia; around 1 in 1,000 people who catch 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 in every 1,000 children infected with measles will die.

Measles doesn’t just affect children. It can also cause premature births in pregnant women who contract it. Immunocompromised people, such as cancer patients and HIV-infected people, are also at increased risk.

CNN: What makes measles so contagious?

Magnifying glass: Measles is one of the most contagious diseases in the world — up to 90% unvaccinated people who come into contact with an infectious individual will also become infected. The measles virus can stay 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 of exposure to fever is an average of about 10 days, and from exposure to rash onset is around 14 days – but can be up to 21 days. In addition, infected people are contagious from four days before the rash begins to four days after. That’s a long period of time where they could infect others without knowing it.

CNN: What caused recent measles outbreaks?

Magnifying glass: It is important to note that this incident in Kentucky is not yet considered an outbreak. Only one person has been diagnosed with measles. This person may have been exposed to many others given the number of people present at this gathering, but we do not yet know if any of these people have been infected.

But let’s look at a recent example of a confirmed outbreak in the United States: November 2022, Central Ohio health officials have sounded the alarm over young children being diagnosed with measles. A total of 85 children fell ill. None of the children died, but 36 had to be hospitalized. Not all infected people were vaccinated 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 we worry it won’t be the last of its kind. CDC study reports vaccination rate for vaccines required among kindergarten students nationwide dropped 95% in the 2019-2020 school year at 93% in the 2021-22 school year. Some communities, however, have rates well below this national average, which can lead to epidemics – not only of measles but also of diseases like polio which can also have serious consequences.

CNN: How effective is the MMR vaccine?

Magnifying glass: The MMR vaccine is a two-dose vaccine. It is recommended that children receive the first dose at 12-15 months of age and the second dose at 4-6 years of age. One dose of the MMR vaccine is 93% effective in preventing measles infection. Two doses are 97% effective.

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

Magnifying glass: The MMR vaccine is an extremely safe and highly effective vaccine and is recognized as a significant public health advance in preventing an otherwise highly contagious disease from spreading and having potentially very serious or even fatal consequences.

Consider that the vaccine was licensed in the United States in 1963. In the previous four years, there were on average more than 500,000 cases measles every year and more than 430 measles-related deaths. In 1998, there were only 89 cases and no deaths associated with measles. This is a huge public health triumph.

Young children should receive the vaccine according to the recommended schedule. Older children and adults who have never had it should also discuss it with their healthcare provider. And clinicians and public health officials in the United States and around the world should redouble their efforts to increase routine childhood immunizations to prevent preventable diseases from making a comeback.