U.S. measles outbreak raises questions about immunity in adults

Public health experts say Americans who were vaccinated against measles decades ago may need another dose of the MMR vaccine. Allison Bartlett, MD, an infectious disease expert at the University of Chicago Medicine, says the "continued vulnerability to infection" is why high-risk adults such as health care workers are routinely advised to get a second dose of the measles vaccine if they have not had one. Anyone vaccinated in the United States between 1963 and 1989 would likely have received only one dose, with many people immunized in the earlier years receiving an inactivated version of the virus. Americans born before 1957 are considered immune because they would have been exposed to the virus directly in an outbreak. At present, Merck & Co. is the only U.S. maker of the MMR vaccine. The company says it has "taken steps to increase U.S. supply" of the vaccine due to the current outbreak.

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