Pennsylvania’s measles outbreak has passed 1,000 cases, making it the largest state outbreak in the US in more than three decades. New York’s governor declared a statewide disaster emergency on Monday as cases rise there too.

Pennsylvania reported 1,004 cases as of October 5, including 198 hospitalizations and five deaths. All five people who died were unvaccinated, according to officials. Lancaster County is the hardest hit, with 391 cases alone.

New York Governor Kathy Hochul declared the emergency after the state recorded 108 cases this year, including 92 since July 15 in under-immunized rural communities across 18 counties. The order expands the pool of health workers allowed to give MMR vaccines and runs through November 4.

The US is having its worst year for measles since 1991, with nearly 3,900 cases reported, according to the Centers for Disease Control and Prevention. Measles was declared eliminated in the US in 2000.

Health officials say the MMR vaccine is about 97 per cent effective after two doses. They urge parents to check vaccination records as the highly contagious virus keeps spreading in communities with low coverage.