US measles count reaches 3,659 as outbreaks spread

As of September 24, the Centers for Disease Control and Prevention had recorded 3,659 measles cases in the United States this year, according to the agency's latest update. That is more than 1,000 cases above the 2,289 cases confirmed for all of 2025, the CDC reported on September 11.

How the national count climbed

By September 11, the CDC had counted 3,294 cases, including 160 new cases in the previous week, most of them in Pennsylvania. The CDC reported five consecutive weeks with increases of at least 100 cases. Of the 2026 cases, 95% were in people who were unvaccinated or whose vaccination status was unknown, and 8% of patients had been hospitalized, compared with 11% in 2025. Children younger than 5 accounted for 18% of cases, and children and teens for 63%.

Pennsylvania's health department reported 676 cases for the year on September 11, after adding 52 cases in two days. More than 99% of the state's cases were in unvaccinated or undervaccinated people, and 124 patients, or 18%, had required hospitalization. Unlike the national pattern, 70% of Pennsylvania's patients were adults. Wisconsin's health department confirmed 163 cases that day, with 155 confirmed and six probable cases tied to an outbreak across Grant, Iowa, and Lafayette counties.

The Kansas Department of Health and Environment said in a September 16 alert that as of September 10, the CDC had reported 3,294 cases and 38 outbreaks. Kansas had recorded two travel-associated cases, both acquired within the United States but outside the state. The department noted that MMR immunization coverage among Kansas kindergarten students was estimated at 90.3%, below the 95% threshold needed for herd immunity, and that exemption rates had risen from 1.0% in 2010-2011 to nearly 4.5% in 2025-2026. Two doses of MMR vaccine are 97% effective against measles, according to the bulletin.

Scientific American reported on September 18 that Pennsylvania had reported its fourth measles-related death that week. The report said confirmed US cases had reached 3,294, and it quoted experts saying vaccination gaps are a common thread in outbreaks. Walter Orenstein, an epidemiologist, said populations need vaccination rates of 95% or higher to achieve herd immunity.

New CDC surveillance data for the week ending September 12, published through the National Notifiable Diseases Surveillance System, showed 3,063 indigenous measles cases nationwide, a 123% increase over 1,374 cases through the same week in 2025, Global Biodefense reported on September 23. The NNDSS figure of 3,063 covers indigenous cases reported by states for that week, while the CDC's September 11 weekly update counted 3,294 total cases, including 16 among international visitors. South Carolina reported 686 cumulative indigenous cases and Pennsylvania 649, together accounting for roughly 44% of indigenous cases nationally; Utah reported 531. That week, 76 of 101 new indigenous cases were in Pennsylvania. The report noted these figures are provisional and subject to revision.

Pennsylvania deaths and federal counting

Pennsylvania's outbreak began in late April, PennLive reported. On September 24, PennLive reported that the Pennsylvania Department of Health had confirmed 835 measles cases in 39 counties, with four deaths and 164 hospitalizations. The deaths involved two infants from Lancaster County who were not old enough for vaccination, a 40-year-old woman from Jefferson County, and an 18-year-old man from Mifflin County; the adults had not been vaccinated and died in September. The CDC website that day listed one measles death nationally, with a note that the count can change and that the agency is collaborating with CSTE, the Council of State and Territorial Epidemiologists, on a standard definition for measles deaths. PennLive reported that Pennsylvania Governor Josh Shapiro said US Health Secretary Robert F. Kennedy had helped lower vaccination rates and told staff not to include Pennsylvania's deaths. In the first three weeks of September, providers in Pennsylvania administered more than 38,000 MMR doses, compared with a typical month of about 25,000; August had more than 49,000 doses.

On September 25, AJMC reported that the CDC's September 24 update listed 3,659 cases. A systematic review of US measles outbreaks since 2000, posted to medRxiv and not yet peer reviewed, estimated an average public health response cost of $43,204 per case, according to AJMC. The report also noted that most insurers are required to cover vaccines only when they carry an ACIP or CDC recommendation, and an August executive order that leaves MMR on the routine schedule but moves other childhood vaccines could shift costs to families. Merck, the manufacturer of an MMR vaccine, stated that no published research supports any benefit from giving the components separately.

The national totals from the NNDSS are provisional and may be revised as delayed reports arrive. The CDC notes the death number can change as it receives more data and finishes reviews.