The United States is experiencing its most serious measles crisis in decades, with Pennsylvania reporting four measles-associated deaths in 2026 as outbreaks continue spreading across the country.
The deaths represent a striking reversal for a disease that was declared eliminated from continuous domestic transmission in the United States in 2000.
Pennsylvania reported two additional deaths in September: a 40-year-old woman and an unvaccinated 18-year-old. The teenager died from acute disseminated encephalomyelitis, or ADEM, a rare but severe neurological complication associated with measles.
Two infants with measles had previously died in Pennsylvania in August. The infants were too young to receive the measles, mumps and rubella vaccine under the standard vaccination schedule.
According to Pennsylvania health officials, none of the four people had been vaccinated.
Those deaths make 2026 the deadliest year associated with measles in the United States since 1992. Together with deaths reported in 2025, the country has recorded seven measles-associated fatalities over two years—more than the combined reported total during the previous three decades.
The deaths are occurring amid a dramatic resurgence of the virus.
By mid-September, Pennsylvania had recorded nearly 700 infections across 38 counties. Nationally, the outbreak has spread much further.
The Centers for Disease Control and Prevention reported more than 3,000 confirmed cases across dozens of jurisdictions by September, making 2026 the country’s worst year for measles infections since 1991.
The situation also highlights an unusual disagreement over how measles deaths should be officially counted.
Pennsylvania health authorities have classified the four deaths as measles-associated. However, Health Secretary Robert F. Kennedy Jr. has questioned whether measles should be considered the underlying cause in some of the cases.
Federal officials said measles deaths would be reported after the National Center for Health Statistics identifies measles as the underlying cause.
The CDC is also developing a standardized definition for classifying measles deaths.
Beyond the disagreement over statistics, the resurgence reflects a broader public-health challenge: declining vaccination coverage.
Measles is among the world’s most contagious infectious diseases, but vaccination is highly effective at preventing it. Maintaining vaccination coverage of roughly 95% is generally considered necessary to provide strong community protection and reduce the risk of sustained outbreaks.
U.S. kindergarten MMR vaccination coverage has fallen below that level.
The decline is not caused by a single factor. Public-health experts point to growing vaccine exemptions, barriers to healthcare access and misinformation about vaccine safety. The result is increasingly large pockets of susceptible people where an imported measles infection can spread rapidly.
The consequences can be serious.
Although many patients recover, measles can cause pneumonia, brain inflammation and other potentially life-threatening complications. Infants and people with weakened immune systems are particularly vulnerable.
The growing outbreak is also creating international consequences.
The United States eliminated endemic measles transmission more than a quarter-century ago, but international health authorities are expected to review whether continued transmission could jeopardize the country’s elimination status.
The 2026 outbreak therefore represents more than an unusually large increase in infections.
It demonstrates how quickly progress against a vaccine-preventable disease can erode when immunity declines across communities.
After decades in which measles deaths became extraordinarily uncommon in the United States, their return is serving as a stark reminder that eliminating a disease does not mean the threat permanently disappears.
