Cases have more than doubled since August as a dispute with federal health officials over the death count continues.
Pennsylvania has confirmed a fifth measles-associated death this year, as the number of infections approaches 1,000 amid a rapidly growing outbreak across the state.
The Pennsylvania Department of Health announced on Wednesday that an unvaccinated resident of Lancaster County who tested positive for measles had died.
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The department said 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 US is currently seeing the worst measles outbreak in the country since 1991, with several deaths reported over the last couple of years.
Measles was declared eliminated in the US 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 latest death is the third associated with measles reported in Lancaster County this year.
Located in the south-central part of the state, Lancaster County is considered the centre of Pennsylvania Dutch Country, home to the nation’s oldest Amish and Mennonite communities. Both communities 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 growing outbreak has prompted the administration of Governor Josh Shapiro to expand vaccination efforts and public health outreach.
Protection is most commonly conferred through a combination injection known as the measles, mumps and rubella vaccine, or the MMR shot.
According to Pennsylvania’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 that two doses of the MMR vaccine are about 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 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.
But 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 the social media platform X on August 26.
Infectious disease experts warn that the dispute over how to classify the deaths puts the CDC at odds with a longstanding approach to tracking the consequences of measles. Epidemiologists have told Al Jazeera that tracking “measles-associated” deaths has long been a standard used by the World Health Organization and the CDC.
The latest death comes as Pennsylvania officials continue to seek additional federal assistance with the outbreak.
In its push for greater epidemiological support, the state requested an Epi-Aid investigation – used for urgent disease outbreaks and other disasters – from the CDC earlier this month, as cases continue to spread.
