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U.S. Measles Cases Reach 30-Year High as Outbreaks Spread Across Multiple States
Just the facts
Driven by significant disease clusters in Arizona, South Carolina, and Utah, the nationwide outbreak expanded as Delaware declared its first outbreak in over a decade with five confirmed cases in Kent County. Delaware medical officials reported that the state's kindergarten vaccination rate for measles, mumps, and rubella (MMR) declined from 98.5 percent in 2016 to 94.1 percent, falling below the 95 percent threshold required for herd immunity. Health department personnel in Delaware vaccinated more than 60 individuals at public clinics and mobile sites following initial case identifications. Federal health guidelines note that two doses of the MMR vaccine provide approximately 97 percent effectiveness against transmission.
Why this is news
Public health authorities across the United States reported that confirmed measles infections reached 2,371 by the end of July 2026, marking the highest annual case count in the nation in 30 years. The surge in cases prompted state and local health departments to deploy mobile vaccination units and initiate contact tracing to contain regional clusters.
Developments timeline
- Health and Human Services Secretary Robert F. Kennedy Jr. publicly urged American parents to vaccinate their children with the MMR vaccine, as total confirmed U.S. measles cases reached 2,371 in 2026.
Sources
This summary is compiled strictly from the original reporting below.