Two Americans have died from measles, the first such deaths this year in the US, as the country grapples with the highest number of cases in more than three decades.

Health officials said on Tuesday that the two Pennsylvania residents were both unvaccinated residents of Lancaster County.

Pennsylvania has been one of the hardest-hit states this year, with 393 measles cases across 28 counties so far.

Lancaster County, in the south-eastern part of the ‌state, has had 185 cases, but these were the first measles deaths recorded in the state in 35 years.

So far this year, the US has had 2,777 confirmed measles cases, a disease that had been largely eradicated in the country.

Among the factors contributing to the increase in infections is the declining vaccination rates.

Vaccination rates of 95% or higher can prevent outbreaks by creating what is known as herd immunity that protects people unable to be vaccinated.

Two doses of the Measles-Mumps-Rubella shot provide 97% protection against the virus.

Children typically first receive the vaccine when they are 12 to 15 months old and again at age four to six years of age.

According to Pennsylvania Department of Health data for the 2025-2026 school year, 93.2% of Pennsylvania kindergarten-age children had received the required two doses of MMR vaccine, down from 93.7% during the 2024-2025 school year.

In Lancaster County, 87.6% of kindergarten students received the required two MMR doses during the 2025-2026 school year.

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The number of US measles cases in 2026 is the highest in a single year since the major resurgence between 1989 and 1991, when 55,000 infections and 123 deaths were recorded.

"Because measles was largely eliminated in the Commonwealth for more than three decades, people are not familiar with this disease and don't fully understand the potential severity of the illness," said Pennsylvania Secretary of Health Debra Bogen.

Health Secretary Robert Kennedy Jr and President Donald Trump have in the past promoted a long-debunked link between vaccines and autism, contrary to established ‌scientific evidence.

Earlier this month, Mr Trump issued an executive order calling for a reduction in recommended childhood vaccines.