A writer for Popular Science breaks down the science and history behind the measles vaccine.

You probably assume that if you got the measles shot as a kid (it’s now combined with mumps, rubella, and sometimes varicella to make the MMR or MMRV vaccine), you’re immune to measles. Period. Surprise! You might not be.

The measles vaccine is pretty amazing—with the recommended two doses, it prevents 97% of cases, and with just one dose it still covers you 93% of the time. But it’s also possible to lose your immunity over time, or for the vaccine to have simply not given you a strong enough protection in the first place.

In that study of 970 measles cases, 40% were in people who had gotten the shot. Getting a vaccine doesn’t always mean you’re immune, so if you’re at all anxious talk to your doctor about getting a test called a titer, where they check your blood for antibodies against the measles vaccine to make sure it worked. And really, you should get the titer no matter what, because you never know.

Read the rest at www.popsci.com