Why Mumps And Measles Can Spread Even When We're Vaccinated

More than two months ago, a nasty mumps virus triggered fever, headache and painfully swollen glands among a handful of students at Ohio State University. Now the outbreak has ballooned to 234 cases at last count, and has spilled into the surrounding community in Columbus, Ohio.

"Columbus officials are calling it the city's biggest outbreak since the development of the mumps vaccine in the 1940s," WOSU reporter Steve Brown tells Shots. "It even pushed them to open a new clinic."

So far, most of those infected are students or workers at Ohio State, Brown says. And here's what's surprising: Many of those who got sick had previously been immunized against mumps via one of the top weapons against childhood diseases: the MMR vaccine. That's a two-dose shot most of us got when we were kids to protect against three diseases — measles, mumps and rubella.