From January to Feb. 20, 2019, the United States has recorded at least 159 cases of measles in 10 states.

Amid surging cases of the viral disease, individuals who have not been vaccinated are urged to be immunized. Adults who had their vaccination as a kid may also consider getting another dose.

Issues With Old Measles Vaccines

The measles vaccine became available in 1963, but one of the main versions used at the time was an inactivated, killed version of the virus. Those who received the killed virus could get a strange disease when they are exposed to the wild measles virus. Researchers call this atypical measles syndrome.

There were only 600,000 to 900,000 people who received the outdated vaccine but the problem is that most people do not know if they had this shot.

It was not until 1968 when a live, attenuated version became the exclusive vaccine administered across the United States.

A less effective version of the live vaccine, which was derived from the original virus isolated from 12-year-old David Edmonston, was also administered between 1963 and 1975. CDC experts said an estimated 18.9 million doses of the shot were administered during this period.

Who Needs Revaccination?

Those who received the standard two doses of the measles, mumps and rubella (MMR) vaccine after 1967 are considered protected against measles for life. People who are uncertain if they received the live or killed version of the measles vaccine in the 1960s are urged to be re-immunized.

People born before 1957 were born in an era when the virus was so prevalent they are they are considered immune. Most of them are believed to have been naturally infected through measles outbreaks, but there are still some who are not immune to the virus.

"We now recommend to people that are traveling abroad that are born in this time period of '57 to early '70s that they should be re-vaccinated when traveling overseas to areas that may have more measles," said Roy Buchinsky. from University Hospital in Ohio.

For those who are uncertain, doctors can now check a person's immunity levels with a blood test that can detect antibodies that fight the measles virus.