The U.S. is in the midst of the worst measles resurgence in decades. Recent outbreaks in several states and exposures in places like bars, sports stadiums and on public transit have some people questioning the safety of travel or how they should prepare for upcoming plans.
The Centers for Disease Control and Prevention lists over 3,600 confirmed measles cases in the U.S. as of Sept. 24 — and two deaths as of Sept. 28. Almost all of those cases have been among unvaccinated individuals.
The CDC notes the number of deaths is subject to change as more information becomes available and after it completes more reviews. It's important to note that the Pennsylvania Department of Health has counted four measles-associated deaths so far. The CDC has disputed whether measles actually caused those deaths.
In the last two weeks, Pennsylvania, Ohio and New York have had the most cases, according to the Johns Hopkins Bloomberg School of Public Health U.S. measles tracker.
The true number of cases across the country is likely higher, according to Dr. Paul Offit, director of the Vaccine Education Center at the Children's Hospital of Philadelphia and a professor of pediatrics at the Perelman School of Medicine at the University of Pennsylvania.
"I think if anything, we're underestimating how many people are actually being exposed, and how many people are being infected, and how many people are being hospitalized and dying," he said.
He said that's because many children, parents or adults may not seek medical care if they get infected.
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Dr. Kalyani McCullough, who leads the Vaccine Preventable Disease Epidemiology & Control Section of the Immunizations Branch of the California Department of Public Health, said it's important for people to know that measles is not "just a fever and a rash."
"It can affect a lot of different parts of the body, and it can have long-lasting effects as well," she said. "Both with immune amnesia, which means that the measles virus can actually reduce immunity to other infections after being infected with measles."
"So I think it's just important for people to realize that getting measles can have some pretty serious consequences," McCullough said.
How do you protect against measles?
People who've had two doses of the MMR vaccine are considered protected against measles.
The disease is highly contagious. It spreads through the air when an infected person coughs, sneezes or breathes. And you don't have to come in direct contact with someone who has measles to get infected; you just have to be within their airspace within two hours of them being there.
Offit said one person with measles can infect about 15 to 18 other people, if they're susceptible. Offit says "susceptible," in this case, means people who've either never had measles, or who are unvaccinated.
For people in that category, up to 9 out of every 10 exposed will get measles.
What does it mean if there have been measles exposures in my state?
Some states that aren't currently experiencing large measles outbreaks have notified residents of possible exposures.
While an outbreak is a group of cases in one area during a certain time period, an exposure is when a person comes into contact with someone who has measles, according to George Mason University College of Public Health epidemiologist Amira Roess.
The California Department of Public Health notified people of potential exposures after an infected and unvaccinated train and bus passenger traveled across the U.S. and through multiple California counties.
The City of St. Louis Department of Health also encouraged residents to monitor for symptoms after an individual who visited local bars and a sports stadium tested positive for measles.
Measles can be difficult for epidemiologists to track because symptoms — like a fever, cough and rash — usually begin seven to 14 days after a person is exposed or as late as 21 days later.
Once a person is confirmed to have measles, epidemiologists interview that person and try to figure out the places they visited and people they saw while they were contagious. In the case of measles, that's typically four days before the telltale rash appears, according to McCullough.
"So it's a really labor-intensive process," she said.
She said anyone exposed to measles is usually advised to seek medical advice and isolate themselves if they develop symptoms within three weeks of exposure. People who are unvaccinated may be asked to quarantine and may be monitored by public health officials to see if they get sick.
What should I do if I'm traveling soon?
All the experts who spoke to NPR said the first and most effective step to protect yourself against measles is to make sure you're fully vaccinated.
That means having had two doses of the MMR vaccine — commonly done in childhood. You can check with your healthcare provider if you aren't sure about your vaccine status. They may recommend a booster depending on your records and recent health.
Offit said this recommendation holds for travelers coming into the U.S. from other countries as well.
"I think anybody who is traveling from another country into the United States should make sure they're up to date on their vaccines, because it's dangerous to be in the United States now if you are not fully immune to measles," he said.
Offit noted many people who are immunocompromised cannot be vaccinated if they haven't been already. Those people may rely on herd immunity — protection from a disease when a certain percentage of people in a community are vaccinated. For measles, this threshold is 95%. Last school year, kindergarten vaccination coverage dipped to 92.4%, according to the CDC.
Children typically get their first dose of the MMR vaccine at around 12 months. But McCullough says if parents are planning to travel internationally with infants or babies 6-11 months old, the CDC's recommendation is to get an early dose of the vaccine.
But the experts we spoke to said that if you have your vaccines, you don't need to worry.
"If you've been relatively healthy and you are up to date on your vaccines, and you are up to date on your doctor's visits, then you will be fine," Roess said. "I'm not worried about those individuals."
Roess also said people can wear masks in busy areas if they are concerned.
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