(BSS/AFP) - Health authorities in the eastern US state of Pennsylvania have confirmed a fourth death linked to measles, as the nation faces the largest outbreak of the vaccine-preventable disease in decades.

All four deaths occurred in unvaccinated individuals, state health officials said.

"My thoughts are with the two families who lost loved ones to this highly contagious virus, as Pennsylvania faces the worst measles outbreak in more than three decades," said state health secretary Debra Bogen.

The latest death was of an 18-year-old, according to local medical examiners, adding to two infants who were too young to be vaccinated and a 40-year-old.

Three other measles-related deaths, including two children, were recorded across the United States last year, when the current outbreak began.

The Pennsylvania deaths have prompted a heated debate between the state`s Democratic governor, Josh Shapiro, and President Donald Trump`s vaccine-skeptic health secretary, Robert F. Kennedy, Jr.

"This serious situation continues to be made worse by RFK Jr. playing games with public health and safety," Shapiro wrote in an X post Tuesday, adding "it`s long past time" for Kennedy to "stop stoking vaccine skepticism and misinformation."

Shapiro noted there have been to date 693 recorded cases of measles in Pennsylvania alone. More than 3,290 cases of measles have been recorded across the US since early 2026.

The governor also accused Kennedy of ordering federal officials at the Centers for Disease Control and Prevention (CDC) "to not report these Pennsylvania deaths, presumably because it doesn`t fit his narrative."

Kennedy denied that allegation in a response on X, and accused Shapiro of politicizing the "outbreak instead of implementing a unified public health response."

"I have repeatedly stated that MMR vaccination is the most effective way to prevent measles," Kennedy said, referring to the vaccine for measles, mumps and rubella.

Measles cause fever, respiratory symptoms, skin rashes and can have serious complications, including pneumonia, brain damaging inflammation and death.

The disease was considered eliminated in the United States in 2000, thanks to vaccination, but has made a strong comeback in recent years amid declining vaccination rates and a backdrop of growing mistrust of health authorities.

Non-medical exemptions to vaccination have surged since the Covid-19 pandemic, allowing Americans to avoid the shots by invoking religious beliefs or other philosophical reasons.

Before a vaccine was developed in the early 1960s, measles killed hundreds of children every year in the US, and continues to cause tens of thousands of deaths globally.