(Bloomberg) — The US has confirmed 3,134 measles cases so far this year, driven by a growing outbreak in Pennsylvania linked to two deaths that started a feud between the governor and the nation’s top health leader.
The US Centers for Disease Control and Prevention confirmed 231 new cases in the week ending Sept. 3. The nation is already at the highest levels since 1991, the last year with more cases, which occurred prior to the formal elimination of the disease.
Pennsylvania has recorded 577 infections and 98 hospitalizations as of Friday, according to the state’s health department. Most of the infections are centered in Lancaster County.
Last month, the state reported two measles-associated deaths, the first in the US this year. On Aug. 28, the CDC delayed its regular weekly update of case data. The agency’s site was then changed to say it was investigating the deaths — an unprecedented change that was ordered by Health and Human Services Secretary Robert F. Kennedy Jr., Reuters reported. The CDC update posted Friday still did not include the two deaths.
The CDC said Friday that it is working with the Council of State and Territorial Epidemiologists to standardize how measles deaths are classified. The CDC partners with the organization to develop case definitions for infectious diseases, but the agency has not updated its measles case definition since 2013.
It’s unusual to revisit reporting criteria unless there is a new laboratory test or a better understanding of the disease, said Jennifer Horney, an epidemiology professor at the University of Delaware.
“There doesn’t appear to be any real science-based reason for changing the case definition,” she said. “Going back to revisit these established criteria opens up the potential that there is even less trust in public health and the data that are being provided by public health officials.”
Pennsylvania Governor Josh Shapiro blamed Kennedy for sowing distrust in vaccines that led to a decline in measles, mumps and rubella vaccination rates.
Kennedy — a longtime vaccine critic who has promoted debunked connections between shots and autism — responded by saying drops in MMR rates came before his time as the country’s top health official. He also cited false information about the shot, saying incorrectly that it contains fetal tissue.
The social media jabs continued through the week — sparking confusion about the two deaths and raising questions about whether they were caused by the virus. Kennedy claimed the deaths may have been “fabricated” or from something other than measles.
But Pennsylvania Secretary of Health Debra Bogen pushed back on Kennedy’s assertion. “I have thoroughly reviewed the case investigation information and sadly can confirm that there were two recent measles-associated deaths in Lancaster County,” she said on social media.
The Lancaster County coroner told local news outlet WGAL that one of the deaths was an infant who died from a ruptured spleen and tested positive for measles. Pediatricians generally recommend children receive the first dose of the MMR vaccine after 12 months.
During the 2025 outbreak in Texas, when two unvaccinated children died, Kennedy touted unproven remedies including vitamin A and cod liver oil to curb infections.
Vaccine policy under Kennedy and President Donald Trump has been upended in the past year. Last month, Trump signed an executive order that recommended the MMR combination vaccine be split into three shots, which would be costly and complicated for manufacturers and require more clinic visits to administer.
The CDC says 94% of those with confirmed measles cases this year are either unvaccinated or have an unknown vaccine status.
