More than 3,600 measles cases have been recorded in the US so far this year, the highest tally in more than three decades.
Data from the Centers for Disease Control and Prevention (CDC) show 3,659 measles infections have been registered nationwide to date.
It is the most since 1991 and 60 percent more than the last year when 2,289 cases were recorded.
Pennsylvania is the hardest-hit state, recording 850 cases, nearly a quarter of the national total, and four deaths.
Cases have now been reported in 45 states, with only Arkansas, Hawaii, Mississippi, New Hampshire and Nevada yet to record an infection.
Yesterday, the CDC confirmed a second measles-related death in Pennsylvania, a fatality that had not previously been reported by the agency. It is yet to report the other two deaths also reported by health officials in Pennsylvania.
The federal agency has slowed its reporting amid a dispute over how measles-related deaths should be counted between Pennsylvania governor Josh Shapiro and Health and Human Services Secretary Robert F Kennedy Jr.
Shapiro has accused RFK Jr of spreading ‘misinformation’ about measles and vaccines, while RFK Jr has said officials need to confirm measles-linked deaths.
There have been 3,659 measles infections recorded in the US as of September 24 (stock)
Measles is the most infectious disease known to man – for unvaccinated people, nine in ten of those exposed to the virus will get infected.
Spread via droplets from coughs and sneezes, in the early stages of an infection, patients suffer from symptoms similar to the flu before developing a red rash that appears on the face or hairline before spreading across the body.
In serious cases, the disease can cause life-threatening pneumonia or encephalitis, or brain swelling.
Children under five years old, pregnant women and those with weakened immune systems are most at risk from the virus.
Among those who are not vaccinated, estimates suggest about one out of every 1,000 who are infected develop encephalitis while one to three in every 1,000 dies from the disease.
Infections can be prevented by receiving two doses of the Measles, Mumps and Rubella (MMR) vaccine, offered from the age of 12 to 15 months, which slashes the risk of an infection by 97 percent.
To treat the disease, patients may be prescribed medications to ease symptoms or put on an IV drip to prevent dehydration. There is no antiviral drug for the virus.
So far this year, about 95 percent of those infected with the virus have been unvaccinated or have not disclosed their vaccination status.
Recent CDC data showed Pennsylvania had recorded the most measles infections in the nation
Cold-like symptoms, such as a fever, cough and a runny or blocked nose, are usually the first signal of measles
The majority of cases have been in school-age children aged five to 19 years old, 1,577 infections, followed by adults aged 20 and older, 1,407 infections.
There have been 327 hospitalizations, including 91 among children under five years old.
Nationwide, South Carolina has recorded the second-highest tally of infections, at 670 cases to date, followed by Utah, 535 cases, and Texas, 192 cases, and Virginia at 178 infections.
No further details were given by the CDC on the measles-linked fatality except that it was recorded in Pennsylvania.
The four fatalities recorded in Pennsylvania were in two infants in Lancaster County, an 18-year-old in Mifflin County and a 40-year-old in Jefferson County.
It comes after a study warned that there was a risk of a major new outbreak of measles happening in Florida.
So far this year, the state has recorded 148 infections, the seventh-highest tally in the nation and an 18-fold rise on the eight cases it reported last year.
Currently, 88.9 percent of Florida kindergarteners were fully vaccinated with the MMR shot for the 2025 to 2026 school year, per the CDC.
In a new study, researchers modeled measles transmission in Florida and concluded that the state’s current MMR vaccination coverage may already be below the level needed to prevent the virus from spreading.
Researchers created a model of measles transmission using data from the 2025 outbreak in Gaines County, Texas. In that year, Texas was the hotspot for measles infections in the US, recording 803 cases.
They then applied the data to Florida, using state-specific factors such as population structure and vaccination coverage to model how measles could spread in the state.
In a worst-case scenario, the model showed that if MMR vaccination among children fell to 82 percent, a major measles outbreak could occur within three to five years.
Smaller outbreaks could then follow more often and continue for decades. Even if vaccination coverage remained at 88.9 percent, the model showed that outbreaks could continue.
The researchers said Florida may already be starting from a vulnerable position, estimating that current MMR vaccination coverage is below the level needed to prevent measles from spreading for long periods.
