“MMR” stands for measles, mumps, and rubella, three distinct viral illnesses. In the 1960s, scientists developed vaccines for each individual disease, but it wasn’t until 1971 that pharmaceutical giant Merck licensed microbiologist Maurice Hilleman’s trifecta and released it to the public. The vaccine has minimal side effects, namely pain or redness at the injection site. One in a million people may suffer from a severe allergic reaction, typically within a few minutes of injection. This can have serious consequences, like febrile seizures. But the benefits are profound: “before measles vaccination was widely available,” the European Centre for Disease Prevention and Control reports, approximately 2.6 million children died every year from measles. In 2012, it was down to 122,000.