US CDC Develops Standard Definition for Measles Deaths as Cases Continue to Rise
Washington, September 22, 2026: Health authorities in the United States are working toward a standardized method for determining and reporting deaths associated with measles as the country continues to deal with a significant rise in infections.
The U.S. Centers for Disease Control and Prevention (CDC) is collaborating with the Council of State and Territorial Epidemiologists (CSTE) to establish a common case definition for measles-related deaths. The objective is to make reporting more consistent across states and territories and improve national disease surveillance.
Measles infections continue to increase
According to the CDC’s latest available data, 3,294 confirmed measles cases had been reported in the United States as of September 10, 2026. The figures are preliminary and can change as health authorities reconcile reports.
Pennsylvania has been particularly affected. Reuters reported on September 21 that the state’s health department had recorded 792 measles cases, an increase of 25 cases from the previous Friday.
Why a standard definition matters
Different jurisdictions can use varying criteria when determining whether a death should be classified as measles-associated. A standardized definition could help health departments apply consistent criteria when investigating fatalities.
The CDC says its work with CSTE is intended to promote consistent classification and reporting of measles deaths across jurisdictions. The agency has also said that national death reporting will be updated as additional information and reviews become available.
Vaccination coverage remains an important concern
The CDC reports that MMR vaccination coverage among U.S. kindergarteners declined from 95.2% in the 2019–2020 school year to 92.4% in 2025–2026. The agency notes that coverage above 95% generally provides stronger community protection against measles.
The decline has left an estimated 280,000 kindergarten-age children at risk during the 2025–2026 school year, according to the CDC.
Pennsylvania outbreak draws attention
Pennsylvania’s outbreak has also generated disagreement over how some reported deaths should be classified. Reuters reported that the state had identified four measles-associated deaths by September 15, while federal authorities were reviewing the classification approach.
Pennsylvania subsequently requested CDC assistance as its outbreak continued to expand.
The debate makes consistent medical and epidemiological definitions particularly important because public-health authorities rely on accurate mortality and infection data when assessing an outbreak.
What happens next?
The CDC’s standardized definition could provide health departments with a common framework for evaluating suspected measles-related fatalities. Until the review process is completed, the agency says its reported figures may change as additional information becomes available.
For the United States, the continuing increase in measles infections and the decline in childhood vaccination coverage have placed renewed attention on disease surveillance, outbreak response and immunization.
The information in this article reflects available reports and CDC data as of September 22, 2026; outbreak figures are preliminary and subject to revision.
