Are you protected from measles? It may depend on when you were born

Adding to the uncertainty, some adults simply don’t know their vaccination status or have long lost their documentation, Cullen said. The history of the measles vaccine has also prompted questions about how people of different ages have been vaccinated: Not only has the recommended number of doses changed over the years, but so has the vaccine itself.

Several years ago, he recalled, a case of measles popped up in Fairbanks, Alaska — the state’s first case in years. Worried about having been exposed and uncertain about whether they were properly vaccinated, patients of his who had traveled there asked for a dose of the vaccine, just in case. (When given within three days of exposure to the virus, the vaccine may offer some protection or make the illness milder, according to health officials.)

Although Alaska hasn’t seen any cases this year, health officials issued an alert following a declaration of emergency in nearby Washington state, which has confirmed dozens of cases in 2019.