Cases of measles have reached a 20-year high in several New York counties amid an outbreak that threatens to reach epidemic proportions, experts say.
At least 160 people have been infected by the virus, which typically strikes children, in New York and unusual outbreaks have been reported internationally.
The worst affected areas so far are Rockland County – where 105 cases have been reported – and an Orthodox Jewish neighborhood in Brooklyn, where at least 55 have been infected.
Meanwhile, 25 other states have reported outbreaks, with numbers climbing particularly high in Oregon and Washington.
Measles is only preventable by vaccination, and health officials in the worst affected areas are scrambling to speed up shots schedules in the most blighted areas.
Among other countries, Israel has seen a recent resurgence in measles.
In October, the sudden uptick in cases in New York City was linked to an unvaccinated traveler from Israel.
Though the details of the Oregon and Washington cases have not been released as publicly, the Washington outbreak was traced to an unvaccinated child who had traveled to the state from another country.
The measles vaccine was introduced in the US in 1963 and, ever since, the virus has been a minimal threat.