The US Centers for Disease Control and Prevention has changed the way it counts and reports measles deaths, a shift that comes as Pennsylvania continues to confirm cases in an ongoing outbreak. The change coincides with a third apparent measles related death in the state, reported by a local coroner on Sunday.

The CDC has moved from using the National Notifiable Diseases Surveillance System, previously described by the agency as the mechanism through which data flows from local jurisdictions and states to federal authorities, to data drawn from the National Center for Health Statistics. The change was announced through a note published on the CDC's website on 4 September.

Debra Houry, a former CDC chief medical officer, described the move as puzzling. She said the change did not make sense, explaining that the National Center for Health Statistics system is designed for high quality, long term mortality trend analysis rather than for confirming individual cases.

HHS spokesperson Emily Hilliard said the CDC will report measles deaths once the National Center for Health Statistics records measles as the underlying cause of death in its data. The CDC has placed an asterisk beneath its published death tally, with an accompanying note stating that the centre currently holds no death records from 2026 that list measles as the underlying cause.

Pennsylvania officials have confirmed two measles associated deaths so far this year, involving a newborn and a six week old infant. A third death was reported on Saturday, involving a 40 year old woman in Jefferson County. Greg Furlong, the county's coroner, confirmed the death and said it was linked to probable measles.

The woman was unvaccinated and had chronic obstructive pulmonary disease requiring continuous oxygen support, conditions that made her more vulnerable to complications. She had not sought medical care for her infection before her condition deteriorated. She displayed the characteristic measles rash along with other symptoms, and a close contact of hers had recently tested positive for the virus. A nasal swab was undergoing testing at the time of reporting, with results expected within days, though the death was being classified as probable measles related due to her epidemiological link to a confirmed case. Furlong said he believed she would have survived without the measles infection, despite her existing health conditions.

Furlong also addressed the wider public health picture, saying that maintaining a measles immunisation rate of at least 95 per cent is essential to protecting those who cannot be vaccinated, including infants under six months old and pregnant people. He expressed hope that the case might prompt more unvaccinated people to get immunised. He also said he believed the official case count understated the true scale of infections in the state.

As of Friday, Pennsylvania had recorded 676 confirmed measles cases. Once the state health department completes its investigation into the latest death, including the results of the nasal swab, it will notify the CDC accordingly.

HHS Secretary Robert F Kennedy Jr had not commented publicly on the third death at the time of writing, instead posting on social media about topics including fitness, Medicaid and Medicare fraud, and screen time. Kennedy had previously disputed claims regarding the first two deaths without providing supporting evidence, and had asked CDC Director Erica Schwartz not to include them in the agency's official tally. The CDC changed its data source for measles deaths the day after this request was reported. Kennedy spent close to two decades leading Children's Health Defense, an organisation known for anti-vaccine advocacy, and has a history of making unsubstantiated claims about vaccines.

Despite this context, Hilliard said the CDC's recommendation for the MMR vaccine remains unchanged, and reiterated that Kennedy has repeatedly stated that MMR vaccination remains the most effective way to prevent measles infection.

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