A 40-year-old woman has died from measles complications in Pennsylvania, marking the state’s third measles-associated death this year as the U.S. experiences its worst resurgence of the highly contagious disease in 35 years.

At least 676 measles cases have been confirmed in 37 counties in Pennsylvania so far this year, state health officials have reported. The outbreak has hospitalized 124 people in the state. Of the confirmed cases, fewer than 1% had been fully vaccinated, officials said.