Getting vaccinated is the most surefire way to prevent catching the disease, as the CDC reports that the vaccine is 99 percent effective.
While about 96 percent of U.S. kindergarten-age children are vaccinated, there are, increasingly, pockets of people across the country who opt out of vaccines for personal or religious reasons.
Though state laws impose vaccinations requirements on schools, with some options available to opt out, many summer programs make their own choices about whether to require vaccines.
At the National Outdoor Leadership School, director of risk management Drew Leemon said neither staff nor students are required to be vaccinated. He added that NOLS is watching the measles situation.
Leemon said some students, though very few, are not vaccinated for religious reasons. NOLS operates programs for people 14 years old and older in the U.S. and abroad, and is running a trip in Europe for the first time this summer.
"We give a lot more advice to our students who are going abroad," Leemon said. "With them, we tell them that they should have their normal vaccinations up-to-date and we refer them to the CDC for any country-specific inoculations that they might need."
Of those who got measles this year, just one had received the full two doses of vaccine that the CDC recommends getting before age 6. The measles vaccine is administered as MMR, a vaccine that protects people from measles, mumps and rubella.
The CDC also found earlier this week that more than one in four U.S. children are not in compliance with official vaccination recommendations because of missed doses of vaccines or vaccine lapses.
That could be the case for some camp staff as well as campers, as Schaffner said teenagers and young adults may have only received one dose and are therefore not "optimally protected."
Still, it's not too late to prepare for summer because the recommended doses can be taken two weeks apart.
"Get 'em vaccinated," Vanderbilt's Schaffner said. "We have two obligations -- to ourselves and to everyone else that we live with."
Camp director Hager said, "You can't be too careful. We even check everybody that comes to camp before they stay over the first night to make sure they don't have lice."