Habanero Pixel/ShutterstockNew York has just declared a state of emergency as measles cases continue to rise. So far this year, the US has recorded 3,887 cases of measles, the highest annual total since 1991. That is about 70% more cases than were recorded during the whole of 2025. In November, the Pan American Health Organization will review whether the US has lost the measles elimination status it has held since 2000.Cases are one thing, but the number of deaths is more complicated. A dispute has developed between the state of Pennsylvania and federal health officials over how many people have died. Pennsylvania, where the outbreak has reached 1,004 cases, has reported five measles-related deaths since late August. But the Centers for Disease Control and Prevention (CDC) has counted two measles deaths nationally in 2026. The CDC has not said where those two deaths occurred, so it is unclear whether either is among the five reported in Pennsylvania. No other state has reported measles deaths this year.What the argument is aboutPart of the disagreement comes down to how a measles-related death is defined. Pennsylvania counts a death as measles-associated if the person had a laboratory-confirmed measles infection and died within 30 days of developing symptoms, unless there is another clear cause of death, such as a car crash. The state says it based its definition on national definitions used for deaths from flu and RSV (a common respiratory infection). The CDC adds a death only once its National Center for Health Statistics has verified that measles was listed as the underlying cause. So there is no agreed national definition of a measles death, though the CDC says that it is working on one.The two approaches can produce different answers in difficult cases, and Pennsylvania has had several. The Lancaster County coroner concluded that a newborn who tested positive for measles died of a lacerated spleen and that measles did not contribute.The same coroner found that a second infant, who had a rare and usually fatal genetic condition, did die of measles. In a third case, the Mifflin County coroner attributed an 18-year-old’s death to acute disseminated encephalomyelitis, a rare and severe neurological complication of measles – so, a confirmed measles-related death.But the dispute has not stayed technical. The CDC initially included the first two Pennsylvania deaths, then removed them after the US Health Secretary, Robert F. Kennedy Jr, questioned whether measles had caused them. Leaving out deaths reported by a state is a departure from the agency’s usual practice.The count matters to both sides: more deaths strengthen the case for vaccination, fewer fit the view that the risk is overstated. RFK Jr, who has for years questioned vaccines but describes himself as “pro-safety” rather than anti-vaccine, has accused politicians of exaggerating the threat from infectious diseases to frighten the public. He also suggested that the Pennsylvania deaths may have been “fabricated by one of the Governor’s hopeful staffers”. Pennsylvania’s Democratic governor Josh Shapiro says Kennedy’s actions and the administration’s rhetoric are harming communities across America. The state has threatened to withdraw a request for CDC outbreak support unless the deaths are recognised – a move the federal health department has described as “political blackmail”Why the count mattersThese are Pennsylvania’s first measles deaths in 35 years, from a vaccine-preventable disease the US declared eliminated in 2000. The fact that measles deaths are happening again shows how far the country has moved from the situation it had achieved through vaccination.That makes the dispute over how many people have died more than a technical argument about definitions. Andrew Pavia of the Infectious Diseases Society of America said the effect of this dispute is confusing the public and undermining trust in the CDC. And this confusion has the biggest impact where vaccination rates are lowest. Measles is so contagious that a community needs more than 95% of people vaccinated to stop it spreading. Below that, outbreaks take hold, and the people most at risk are those who cannot protect themselves, such as babies too young for the vaccine, which is normally given at 12 to 15 months. Across the US, MMR coverage is lower among children who are uninsured or on Medicaid, living below the poverty line or living in rural areas. Averages also hide local gaps. In Lancaster County, 88% of pupils were vaccinated against measles last school year, against 97% across Pennsylvania. These are the communities where clear information about risk matters most. When official figures conflict, it is harder to tell people how serious an outbreak is, and harder to make the case for sending staff and vaccines their way.The UK lost its own elimination status in January, and a child died of measles in Liverpool in July 2025. Only 85% of five-year-olds in England have had both MMR doses, against a 95% target. Coverage also follows deprivation: in 2016-17 England’s most deprived areas had slightly higher MMR coverage than the least deprived, by 2024-25 they were 7.6 percentage points behind. In both countries, health services need accurate, consistent figures to know where those gaps are so protection reaches everyone in proportion to need Ninety-five per cent of people need to be vaccinated against measles for herd immunity to kick in. Efired/Shutterstock What would help?A couple of practical steps could help. A national definition of a measles death, agreed in advance and applied the same way everywhere, would take the question out of individual disputes. Publishing basic details of each counted death, such as state and age group, would let anyone reconcile federal and state figures. Neither requires anyone to concede a wider political argument.There are encouraging signs on vaccination. By mid-July, Pennsylvania’s state health staff had given more than three times as many MMR doses in Lancaster County as in the whole of 2025. And the UK shows that elimination can be won back, having lost its status in 2018 and regained it again in 2021.If the US loses its status in November, that will describe the past year, rather than decide the next one. Closing the local coverage gaps is what matters most, and it is easier when everyone is working from the same numbers.Philip Broadbent receives funding from The Wellcome Trust 223499/Z/21/Z