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In recent years, the resurgence of a virus that caused massive global epidemics every two or three years and caused millions of deaths has been observed. The United States was declared free of this disease in 2000, according to the World Health Organization (WHO).
Since the creation of the vaccine and its global application, contagion levels have decreased and, with that, mortality has also declined. However, outbreaks continue to be reported in certain areas of the world, and this is what is currently happening in the United States.
3,471 cases were recorded through September: Which was the most affected state?
As of September 17, the United States had recorded 3,471 confirmed cases of measles according to the Centers for Disease Control and Prevention (CDC). Of this total, 3,296 infections were related to outbreaks. Cases were reported in 47 jurisdictions across the country.
The main epicenter is in Pennsylvania, the state that is experiencing one of the most serious outbreaks in the country. The state Department of Health reported on Wednesday, September 23, that there were already 835 confirmed cases in 39 counties in this territory.
At the hospital level, Pennsylvania counted 164 hospitalizations related to the disease and four deaths. According to the data gathered by the state, of the 835 infected patients registered, only four were vaccinated.
The 2026 U.S. outbreak far exceeds the previous year’s. Throughout 2025, 2,289 cases had been recorded, compared with the more than 3,400 registered before the end of September this year.
The first measles death confirmed by the CDC: Why did they not confirm the ones reported by Pennsylvania?
On September 23, the CDC confirmed for the first time in 2026 a measles-related death in the national record. However, the agency did not report which state it occurred in nor did it state that it was one of the four deaths recorded in Pennsylvania.
This could have happened for several reasons, but it is mainly due to the criteria used by federal and state authorities. Pennsylvania had already confirmed four measles-related deaths, but the CDC decided to base its national count on death certificates processed by the National Center for Health Statistics (NCHS).
For this reason, the agency is working on a standardized definition to apply the same criterion in all states.
How serious is the outbreak and what measures are being taken?
The severity of the outbreak is defined not only by the number of infections, but also by its spread, hospitalizations, and decline in immunization levels.
Regarding coverage of the MMR vaccine, which protects against measles, mumps, and rubella, it fell from 95.2% in the 2019-2020 cycle to 92.4% in 2025-2026 among kindergarten children. According to the agency, it is estimated that approximately 280,000 children were exposed during the last school year.
Pennsylvania, one of the most affected states, organized 156 temporary vaccination clinics in the affected communities and administered nearly 5,200 doses of the MMR vaccine, as reported through September 23.
According to the Pennsylvania Department of Health, two doses of MMR provide approximately 97% protection against measles and remain the main preventive tool.