Two people have died from measles in Pennsylvania, marking the first fatalities from the disease in the United States this year.
The victims, who were both unvaccinated residents of Lancaster County, are the first people to die from measles in the state in 35 years.
Pennsylvania health officials confirmed the deaths, which occurred about 60 miles outside of Philadelphia, but provided no further details about the patients.
"My deepest sympathies are with the loved ones who are facing this unimaginable loss," Dr Debra Bogen, the state secretary of health, said in a statement.
"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."
Nationwide surge in cases
The fatalities come as measles infections across the US reach their highest level in more than three decades, driven by outbreaks in multiple states.
The Centers for Disease Control and Prevention had recorded 2,777 confirmed cases of measles as of August 20. This is the highest number of infections since 1991, when 9,643 cases were logged, and up from 2,289 cases last year.
Pennsylvania alone has recorded 393 cases across 28 counties so far in 2026.
Health officials in Maryland have also declared an outbreak across three counties, reporting 14 new cases among unvaccinated residents. This brings Maryland's total to 31 cases for the year, with 27 of those in unvaccinated individuals.
In Iowa, the state health department announced on Monday that 17 cases had been reported.
Vaccination rates below threshold
The vast majority of measles cases in 2025 and 2026 have occurred in individuals who have not received both doses of the measles, mumps and rubella vaccine.
The CDC says two doses slash the risk of a measles infection by 97 percent. The vaccine is typically given first between the ages of 12 and 15 months, and again between the ages of four and six.
Nationwide, 92.4 percent of kindergarteners are fully vaccinated against the disease, which is below the 95 percent threshold the CDC says is required for herd immunity.
Vaccination exemptions are also increasing, now standing at 4.2 percent, up 17 percent from 1.6 percent just over a decade ago.
State vaccination rates vary, with Maryland at 96 percent, Pennsylvania at 94.6 percent, and Iowa at 90 percent.
"We want to ensure every Pennsylvanian has the information they need to protect themselves, their loved ones and their communities," Bogen said.
"As a physician, I want to make sure that people understand that the MMR vaccine is safe and provides the best protection we have against measles."
Highly infectious virus
Measles is a highly infectious virus that spreads through the air or via direct contact with infectious droplets. Unvaccinated people have a 90 percent chance of becoming infected if they are exposed to the virus.
Patients are contagious from four days before they develop a rash until four days after it appears. This makes enclosed areas like planes and airports extremely risky locations for disease transmission.
The disease is characterised by a cough, a fever, tiny white Koplik spots inside the mouth, and a distinctive blotchy rash that starts on the face before spreading down the body.
The virus first invades the respiratory system before spreading to the lymph nodes and throughout the body, where it can affect the lungs, brain and central nervous system.
While symptoms can be milder, including achiness, a sore throat and diarrhea, measles leads to pneumonia in roughly six percent of otherwise healthy children, and more often in malnourished children.
It also severely damages a child's immune system, making them susceptible to other potentially devastating bacterial and viral infections they were previously protected against.
In rare instances, occurring in about one in 1,000 cases, the virus triggers brain swelling. This is deadly in roughly 15 to 20 percent of those who develop it, while about 20 percent are left with permanent neurological damage, such as brain damage, deafness or intellectual disability.
Before MMR vaccines became available in the 1960s, measles caused epidemics with up to 2.6 million global deaths every year. By 2023, that number had fallen to roughly 107,000 deaths.
