CHICAGO - Adults in the United States who were vaccinated against measles decades ago may need a new dose depending on when they received the shot and their exposure risk, according to public health experts battling the nation’s largest outbreak since the virus was deemed eliminated in 2000.
People vaccinated in the United States since 1989 would most likely have received two doses of the combined measles, mumps and rubella shot under federal guidelines, and that is still considered the standard for protection. According to the World Health Organisation, 95% of a population needs to be vaccinated to provide “herd immunity,” a form of indirect protection that prevents infection in people too young or sick to be vaccinated. US public health officials have blamed the current outbreak in part on rising rates of vaccine skepticism that have reduced measles immunity in certain communities.
This has occurred even in adults with two documented doses of the vaccine, said Dr Michael Phillips, chief epidemiologist at NYU Langone Health, which serves parts of New York City, a hot spot in the US outbreak.