Pennsylvania has confirmed a fifth measles-associated death this year as the number of infections in the state approaches 1,000.

The Pennsylvania Department of Health announced on Wednesday that an unvaccinated Lancaster County resident who had tested positive for measles had died. The death was reported to the United States Centers for Disease Control and Prevention (CDC).

The state has recorded 943 confirmed measles cases across 39 counties so far in 2026, including 40 new cases since September 28. At least 176 people have been hospitalised.

The latest death is the third measles-associated fatality reported in Lancaster County this year. The county, located in the south-central part of the state, is home to the nation's oldest Amish and Mennonite communities, both of which have under-vaccinated populations.

Pennsylvania announced its first two measles-associated deaths in August, the first measles-related deaths recorded in the state in 35 years. Since then, the number of confirmed infections has more than doubled.

The US is currently experiencing its worst measles outbreak since 1991. Measles was declared eliminated in the country in 2000, but the highly infectious disease has made a comeback in recent years, a trend some experts have linked to a rise in vaccine scepticism.

The growing outbreak has prompted the administration of Governor Josh Shapiro to expand vaccination efforts and public health outreach. According to the state's Department of Health, more than 53,000 MMR vaccine doses were administered statewide in September, more than twice the number given during a typical month. Health experts say two doses of the MMR vaccine are approximately 97 percent effective at preventing measles.

On Tuesday, the CDC confirmed two measles-related deaths in its national tally, though the agency did not identify where the deaths occurred.

The federal count has been at the centre of a dispute between Governor Shapiro and US Health Secretary Robert F. Kennedy Jr. over how measles deaths are classified. Pennsylvania has reported five "measles-associated" deaths, a designation used when a person with confirmed measles dies within 30 days of developing symptoms, unless the death resulted from an unrelated event.

Kennedy, a vaccine sceptic, has accused Shapiro of politicising the deaths and initially questioned whether two deaths reported by the state in August were linked to measles. "The announcement appears to have been premature, and the deaths may even have been altogether fabricated by one of the Governor's hopeful staffers," Kennedy wrote on social media on August 26.

Infectious disease experts have warned that the dispute over how to classify the deaths puts the CDC at odds with a longstanding approach to tracking measles consequences. Epidemiologists have said that tracking "measles-associated" deaths has long been a standard used by the World Health Organization and the CDC.

Pennsylvania officials continue to seek additional federal assistance. The state requested an Epi-Aid investigation from the CDC earlier this month, a mechanism used for urgent disease outbreaks and other public health emergencies, as cases continue to spread.