Why are measles and other “eradicated” infectious diseases coming back?

Measles have made a comeback, with outbreaks in many states. The infection is extremely contagious and can be deadly. Most people getting measles were not vaccinated against it. Adults should get the vaccine if they were born after 1957 and didn’t receive two doses. They should get a booster shot if they received the vaccine between 1963 and 1968, when the vaccine used was not as strong as the one that’s been given since 1968.