Daniel Salmon, the director of the Institute of Vaccine Safety at Johns Hopkins University, told ABC News that the involvement of a foreign individual or an American who recently traveled to a foreign country is "typically" how measles outbreaks start in the U.S.
"Most of the time we don't have indigenous transition of measles" in the U.S., Salmon said. "We do right now, but once this outbreak is taken care of, we'll have no more measles in the U.S."
