How worried should people be about the measles? An expert explains

By Katia Hetter, CNN

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Measles cases are increasing in the United States, with 45 infections reported in 17 states as of March 7, according to the US Centers for Disease Control and Prevention. That’s close to the total of 58 cases documented in the United States in all of 2023.

Globally, a decline in vaccination coverage has contributed to a rise in measles infections and death, the World Health Organization has also noted.

While the US numbers might seem low, measles is one of the most infectious diseases in the world, so it’s worth taking a closer look at how it’s spread, the symptoms and why it’s considered dangerous. A vaccine is available, but how effective is it? Do people need additional vaccine doses? And should people avoid areas that have active measles cases?

To find out answers, I spoke with CNN wellness expert Dr. Leana Wen, who is an emergency physician and adjunct associate professor at George Washington University. She previously was the health commissioner of Baltimore, overseeing investigations for infectious diseases, including measles.

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

Dr. Leana Wen: Measles is an infection caused by a virus, and health experts consider it to be one of the most contagious diseases in the world. The respiratory virus transmits through droplets from the nose, mouth or throat of infected people, which can land directly on someone else’s nose or mouth or be spread through touching contaminated surfaces. Viral aerosols can linger in the air for as long as two hours after an infected person has left the area.

Symptoms of measles include high fever, fatigue, cough, runny nose and conjunctivitis, also called pink eye. People can develop spots inside their mouth, followed by a reddish rash that typically starts on the face and then spreads down their body.

CNN: Why is measles such a dangerous disease?

Wen: For two reasons: the severity of the disease and how easily it spreads.

While many people who contract measles will have symptoms that go away on their own,  some — including previously healthy people — will experience severe complications.

As many as 1 in 5 unvaccinated people who contract measles end up needing hospitalization, according to the CDC. Up to 1 in every 20 children will develop pneumonia, and 1 in 1,000 develop a dangerous swelling in the brain called encephalitis that can lead to seizures. Other complications include deafness and other lifelong disabilities.

Measles can be fatal. According to the World Health Organization, 136,000 people — mostly children — died from measles in 2022.

In addition, measles is so dangerous because of its extremely high level of contagiousness. An unvaccinated person who is exposed to someone with measles has a nearly 90% chance of becoming infected. Measles also has a long incubation period, which means that someone could have measles and not know it for as long as two or three weeks.

CNN: What vaccine can help prevent measles, and how effective is it?

Wen: The measles, mumps and rubella, or MMR, vaccine, is highly effective at preventing measles. Two doses are 97% effective at preventing measles if a person is exposed to the virus. One dose is around 93% effective.

CNN: When should people get the MMR vaccine?

Wen: The CDC recommends that all children receive two doses of the MMR vaccine. The first dose is available to kids ages 1 year to 15 months old, and the second one at 4 years through 6 years of age.

CNN: What about older kids or adults who may not have received the MMR vaccine before?

Wen: Older kids can receive two doses of the MMR vaccine, separated by at least 28 days. Adults without presumed immunity should receive at least one dose, but many are recommended to receive two doses, including university students, people who work in health care and those who plan on traveling internationally.

Adults can be presumed to have immunity if they were born before 1957, according to the CDC. There could also be laboratory testing done through your physician’s office that can confirm immunity through vaccination or infection.

CNN: Should people get a third MMR shot?

Wen: The CDC does not generally recommend additional MMR vaccines for people who are already vaccinated with two doses or have presumptive immunity from prior infection.

CNN: Are there specific considerations for MMR vaccination during outbreaks?

Wen: During measles outbreaks, local and state health departments, in collaboration with the CDC, may issue additional guidance for vaccination. Public health officials may urge individuals who have received just one dose of the MMR vaccine to receive the second dose. The schedule for vaccination may be expedited. For instance, health officials may recommend that an early first dose be given to infants 6 months to 11 months old, and a second dose to children before they turn 4 years old.

There is also something called post-exposure prophylaxis that officials could recommend. Unvaccinated people exposed to someone with measles can receive the MMR vaccine within 72 hours of exposure. This helps to reduce their chance of becoming infected and passing it on to others.

CNN: Should people avoid travel to areas in the US that have measles cases?

Wen: Not at this time, though everyone should ensure that they are up to date on their MMR vaccines, and individuals who are immunocompromised or have other severe underlying medical conditions may seek additional protection from respiratory viruses during their travels.

CNN: Why is it that measles cases appear to be on the rise?

Wen: The CDC estimates that 95% of the population should be vaccinated to prevent measles from further spreading. Unfortunately, the vaccination rate has been declining. According to a January 2023 report, only about 92% of US children have gotten the MMR vaccine by age 2.

Infectious diseases like measles will spread unless our society has sufficient population immunity. It would be such a tragedy to have measles and other diseases return when there are safe and effective tools that have saved many lives.

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