CDC to Send 'Disease Detective' to Pennsylvania as US Measles Cases Top 4,400

The Centers for Disease Control and Prevention is preparing to send a field investigator to Pennsylvania to help contain a measles outbreak that state health officials say has grown past 1,200 cases. According to a CDC spokesperson who spoke to ABC News, Pennsylvania formally requested federal help through the agency's Epi-Aid program, and the CDC will support the state's identified needs and bolster its on-the-ground response.

The deployment comes as the CDC reported 4,410 confirmed measles cases nationwide in its Friday update, with the bulk of them spread across 45 states and Washington, D.C. Eighteen of this year's cases involve international visitors to the United States, the agency said. Pennsylvania has also recorded six measles-related deaths, according to local health officials.

An Epi-Aid is a rapid, short-term field investigation the CDC launches in response to an urgent public health problem. The program supplies resources that can include expanding the workforce available for rapid response and building epidemiologic capacity, the agency says.

State data shows fewer than 1% of Pennsylvania's cases occurred in people fully vaccinated with the MMR vaccine, ABC News reported. That mirrors the national picture: the CDC said roughly 96% of cases involve people who are unvaccinated or whose vaccination status is unknown, while 2% had received a single dose and 2% had received both recommended doses.

Federal guidance calls for two MMR doses, the first at 12 to 15 months and the second between ages 4 and 6. The CDC says one dose is 93% effective against measles and two doses are 97% effective, though vaccination rates have slipped in recent years — 92.4% of kindergartners were vaccinated during the 2025-26 school year, down from 95.2% in 2019-20 before the COVID-19 pandemic.

The agency said Health Secretary Robert F. Kennedy Jr. and CDC Director Dr. Erica Schwartz continue to recommend the MMR vaccine as the most effective way to prevent measles and protect against infection.