Planning a summer trip abroad? Between digging out your passport and booking hotels, find some time to look up your medical records. If you're older than 28 years old, you may need a measles vaccination—even if you were inoculated as a kid.

As Slate explains, prior to 1989, the Centers for Disease Control only recommended that children receive one dose of the measles, mumps, and rubella (MMR) vaccine. But since measles outbreaks were still far from being a thing of the past, health officials revised the guidelines to recommend two doses. They also recommended that travelers going abroad receive a measles booster shot if they had just received one MMR vaccination and had never experienced a full-blown case of the disease.

Travelers who were born before 1957 can ignore this advice, as they were probably exposed to a prior measles epidemic and are thereby immune. But if you were born between then and 1989, check with your doctor (or dig up your medical records) to ensure you’re fully covered. If not, get the shot.

Thanks to the two-dose measles vaccine and a robust vaccination program, the Americas were declared measles-free in 2000. The disease is still prevalent in other countries around the world: Measles has surged across Europe in recent months, as many people there haven’t received the second dose of the two-dose measles vaccine. It’s also common, and even deadly, in developing countries, including parts of Africa and Asia.

Today, measles is relatively rare in the U.S., but imported cases do pop up. Typically, they occur because someone who was either unvaccinated or under-vaccinated traveled abroad and contracted the disease, then brought it home and transmitted it to others who hadn't been immunized.

This raises the question: Why are Americans still going abroad without getting a measles booster shot? As a new study published in the Annals of Internal Medicine shows, many health-conscious travelers who aren't 100 percent measles-immune refuse the shot because they’re not worried about contracting the disease. But judging by the recent measles surge in Europe—not to mention a new measles outbreak in Minnesota that's linked to anti-vaccination campaigns—they should be.

[h/t Slate]