Explainer: During the measles outbreak in the United States, who needs an extra dose of the vaccine?

(Reuters) – The United States is currently experiencing the largest measles outbreak in 25 years. The disease mainly strikes people who have not received the two recommended doses of live measles vaccine.

While the vast majority of measles patients are unvaccinated children, up to 10% of patients in the current outbreak are adults who have received at least one dose of the measles-mumps-rubella vaccine.

The US Centers for Disease Control and Prevention have issued recommendations on when adults may need to request an extra dose of MMR vaccine:

WHAT ADULTS ARE CONSIDERED AT HIGH RISK?

The CDC consider health care workers, university students, adults traveling abroad and those living in communities where epidemics are high risk.

HOW CAN PEOPLE BE INSURED WHERE THEY ARE IMMUNE TO DISEASES?

People born before 1957, when the vaccine became readily available in the United States, are presumed immune because they would likely have been directly exposed to the virus. Blood tests can also confirm immunity.

People who have had a confirmed case of measles would have developed immunity.

Adults in high-risk groups or in areas affected by an outbreak, including parts of New York City, Rockland County, New York; Oakland County, Michigan and parts of California, as well as school-aged children, must have received two doses to ensure their immunity.

Adults who do not live in areas affected by an epidemic and have received at least one dose of the vaccine should also be immunized. This is also true for children who are not yet in school.

The CDC recommends that any adult who has doubts about his immunity be vaccinated.

What about people born between 1957 and 1968?

It depends on the type of vaccine received. People whose written documentation shows that they have received live MMR vaccine do not need to be vaccinated again. Those who received the vaccine inactive, or "killed", need to be vaccinated again because this version has proven ineffective.

ARE THERE ADULTS WHICH A PHYSICIAN WILL ADVISE TO TAKE MACHINE?

The CDC recommends that pregnant women, people with compromised immune systems, or who have received another vaccine in the last four weeks, seek the advice of their doctor before being vaccinated against measles.