Delaware County has zero confirmed measles cases even as Pennsylvania's outbreak crossed 1,004 statewide on Monday, Oct. 5, according to NBC10 Philadelphia. The state Department of Health reported 198 hospitalizations and five deaths since the outbreak began in late April.
But the virus is close. Neighboring Chester County has 84 confirmed cases, the third-highest total in the state behind Lancaster County's 391 and Mifflin County's 118. The Philadelphia region has 95 cases total.
The Philadelphia Inquirer reported Monday that Chester City, which sits in Delaware County, has seen measles vaccination rates fall below the herd immunity threshold. Dale Weiser, clinical services supervisor for Chester County's health department, told the Inquirer the situation is urgent.
"It's going to either burn through all the susceptible people, or we're going to make fewer people susceptible through vaccination," Weiser said. "That's the only way it ends."
What Delaware County data shows
The Delaware County Health Department detected measles in wastewater samples collected in June at the DELCORA Western Regional Treatment Plant in Chester. The plant serves roughly half a million people in the greater Philadelphia area, including parts of the Radnor and Haverford township region. No county residents had a confirmed infection at the time of the June 17 announcement. That has not changed.
Delaware County's kindergarten MMR vaccination rate stood at 94.3% during the 2024–2025 school year, according to the county health department. Public health officials say 95% is needed for herd immunity against measles.
About 1 in 5 unvaccinated people who contract measles will be hospitalized, the county health department said. About 1 in 1,000 could develop brain swelling and possible brain damage.
Statewide vaccination push
Pennsylvania health care providers administered more than 49,000 doses of the measles, mumps and rubella (MMR) vaccine in August and more than 53,000 in September, according to Fox 29. A typical month sees about 25,000 doses.
Fewer than 1% of Pennsylvania's confirmed cases are among people fully vaccinated with the MMR vaccine, according to the Department of Health. The CDC recommends two doses: the first at 12 to 15 months old, the second between ages 4 and 6. Two doses are 97% effective at preventing measles.
Pennsylvania leads the nation in measles cases, according to 6abc. Nationally, the CDC reported 3,887 confirmed cases across 45 states and Washington, D.C., as of Oct. 1. That is the highest U.S. total since 1991.
Of the five Pennsylvania deaths, two were unvaccinated adults, ages 18 and 40. Two were infants too young to have received the vaccine. The fifth was an unvaccinated Lancaster County resident whose age has not been disclosed.
How to check vaccination status
Residents unsure of their vaccination status can check with their health care provider. The Delaware County Health Department says it is safe to get another MMR dose even if a person may already be immune.
The Delaware County Health Department Wellness Line is available at 484-276-2100. The state health department hotline is 877-724-3258. The state's measles dashboard is updated regularly at pa.gov/measles.
