The Allegheny County Health Department is monitoring the spread of measles across Pennsylvania following an outbreak in Lancaster County. There are currently no confirmed cases of the virus in Allegheny County.
Five unvaccinated individuals in Lancaster County tested positive for the virus on Feb. 3. This local activity occurs amid a national surge in measles cases, with 662 infections reported across the United States in January 2026.
The Centers for Disease Control and Prevention reports that 97% of measles cases in the country involve people who are not vaccinated or have an unknown vaccination status. Health officials state that the measles, mumps and rubella vaccine is the most effective prevention method. One dose of the MMR vaccine is 93% effective, while two doses are 97% effective.
Beyond vaccination, health officials warned that measles is considered one of the most contagious viruses on Earth. Approximately 90% of people who are not immune will become infected after being exposed to the virus.
These risks are particularly high for specific populations, including children under age 5 and individuals with preexisting lung disease. Immunocompromised individuals and pregnant women also face increased danger, as the virus can lead to premature births or low-birth-weight babies.
Severe complications from the virus range from ear infections and diarrhea to pneumonia and encephalitis, which involves swelling of the brain. A rare and fatal condition called subacute sclerosing panencephalitis can also occur several years after an initial measles infection.
To mitigate these risks, the Allegheny County Health Department has implemented multiple monitoring strategies. These include wastewater surveillance testing to identify cases early and a daily review of emergency department visits and disease reports.
In addition to surveillance, the department is coordinating with other jurisdictions to identify residents who may have been exposed to the virus through air travel or public events. Officials also assess school immunization coverage annually and provide resources to institutions that report lower vaccination rates.
The Allegheny County Health Department Immunization Clinic is providing MMR vaccines to residents. Community organizations interested in hosting on-site clinics for 10 or more people are encouraged to contact the department for assistance. Residents who believe they or their children have been exposed to the virus should contact their health care provider immediately.
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