The measles outbreak in the U.S. is the worst in 25 years, and the Centers for Disease Control and Prevention is saying that some adults who were vaccinated against the virus decades ago may need a new dose.

According to Time, up to 10 percent of the 695 cases that have been confirmed were in people who had one or two doses of the vaccine.

The CDC also recommends that people who are living or traveling to outbreak areas should check their vaccination status and consider getting a new dose.

Individuals who were vaccinated in the U.S. since 1989 will most likely have gotten two doses of the (MMR) shot which covers measles, mumps, and rubella which is the the standard  for protection.

However, if you were born between 1963 and 1989 you would likely have received only one dose and Americans born 1957 are considered immune, since they would have been exposed to the virus in an outbreak.

If your immunization records are lost, a blood test can show if someone has immunity.