Ben Pratt is a frequent traveler and is planning a trip to India in January. He's getting his shots now to make sure he doesn't get sick while he's away.
"I know friends that have been sick overseas, and I don't want that for me or my companions," he told CBS News.
But new research shows many Americans are traveling abroad without taking this important precaution. According to a study presented this week at an infectious disease conference in San Diego, of the nearly 41,000 international U.S. fliers examined, 16 percent needed the measles, mumps and rubella (MMR) vaccine -- but only about half of them actually got it.
"Most people believe that they've already had their childhood immunizations -- they're just like, 'Oh yeah, I would have had that,' and no further consideration," said Rayann Aziz, Executive Director of Passport Health, the largest provider of travel medicine and immunization services in North America.
This is dangerous, health experts say, because most measles outbreaks in the U.S. are caused by unvaccinated people who are infected overseas.
"Measles is one of the most contagious diseases in the world and even brief exposure can lead to infection," the lead study author, Dr. Emily Hyle, an infectious disease specialist and instructor at Harvard Medical School and Massachusetts General Hospital, said in a statement. "Many travelers heading to developed countries, including those in Europe, might not realize that there are outbreaks of measles occurring in those areas, and they are at risk for becoming ill."
Measles can lead to pneumonia, brain swelling and potentially death.
Another study also presented at the conference found that a hepatitis A outbreak in Mexico earlier this year could have been prevented if the travelers had been vaccinated. The researchers note that consuming contaminated food and water while traveling abroad is the most common way Americans become ill with this virus. It can cause symptoms like fever, nausea, exhaustion, jaundice and stomach pain.
"Even if you're going to Mexico, Europe, anywhere you're traveling, there are probably vaccines that you should check on," said Dr. Amy Edwards, a pediatric infectious disease specialist at University Hospitals Case Medical Center.
Travel health experts recommend anyone traveling overseas should see their doctor for a consultation two months before leaving the country.