STEVE INSKEEP, HOST:
The United States is in the middle of the deadliest measles epidemic in decades. Falling vaccination rates have made communities vulnerable. Some kids need to be vaccinated, and some adults need a second shot. NPR's Maria Godoy reports.
MARIA GODOY, BYLINE: Measles is the most contagious disease known.
ADAM RATNER: It's more contagious than flu or polio or Ebola or any other scary-sounding disease you can think of.
GODOY: Dr. Adam Ratner is a pediatric infectious disease specialist in New York City. He says the virus will rip through communities quickly, seeking out anyone who's not immune and infecting them.
RATNER: That is exactly what we're seeing in Pennsylvania now. And it's what we saw in West Texas last year and in Utah for many months in a row and in South Carolina earlier this year.
GODOY: Each of those states has seen large outbreaks with many hundreds of cases. Nationwide, more than 4,000 measles cases have been reported this year alone. Patsy Stinchfield is executive director of the Measles Collaborative. She says that surge has got many people wondering if they're at risk.
PATSY STINCHFIELD: It's a very common question for people to ask - am I immune? Am I OK? What do I need to do? And that is exactly the right question everyone should be asking themselves right now.
GODOY: The best defense is vaccination. Two doses of the measles, mumps and rubella vaccine is 97% effective, meaning 97% of people will have an immune response.
STINCHFIELD: Two doses will get you the highest antibody protection you can get, and it confers it for a lifelong immunity.
GODOY: But what if you don't know your immunization history or you only got one dose of the measles shot? Should you get another dose? Stinchfield says that depends on several factors.
STINCHFIELD: First of all, when were you born?
GODOY: If the answer is before 1957, you're presumed to be immune because back then, measles was so common, just about everyone got it in childhood.
STINCHFIELD: They survived. They've got immunity.
GODOY: People who were born after 1957 and vaccinated before 1968 may need an additional dose. That's because some people immunized during that time received an early, less effective version of the vaccine.
STINCHFIELD: It didn't work as well.
GODOY: Most people vaccinated before 1989 probably received just one dose of measles vaccine instead of the two doses recommended for children today. Larry Kociolek is a pediatric infectious disease doctor at Northwestern University. He says traditionally, one dose of measles vaccine has been considered enough protection for most adults.
LARRY KOCIOLEK: Unless you have risk factors for developing measles, like you're a healthcare worker, for example.
GODOY: But Kociolek notes that advice was crafted before the recent dramatic rise of measles activity across the country. He says, these days...
KOCIOLEK: If you are living in areas with high measles activity, it does make a whole lot of sense for adults to go ahead and get that second dose.
GODOY: If you're not certain whether you've already had two doses, you could get a blood test to check your antibodies. But he says those tests can be finicky. It's usually simpler to just get another shot.
KOCIOLEK: There is no harm of getting an additional MMR vaccine.
GODOY: After all, it's much better to be protected than infected.
Maria Godoy, NPR News.
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