Pennsylvania is dealing with one of the fastest growing measles outbreaks in the country, and the latest numbers show that the problem is moving well beyond a small cluster in Lancaster County.
By Wednesday evening, the Pennsylvania Department of Health had confirmed 424 measles cases in 2026. 94 of those cases were diagnosed in the previous week alone. New infections have also appeared in counties that had not reported cases earlier in the outbreak, including Westmoreland and Butler counties.
The surge comes days after state officials confirmed two measles-associated deaths involving unvaccinated Lancaster County residents. They are the first deaths associated with measles in Pennsylvania in 35 years and the first reported in the United States this year.
One of The Deaths Involved an Infant
State health officials confirmed on Wednesday that one of the two people who died was an infant.
The case has drawn additional scrutiny because records from the Lancaster County Coroner do not describe measles as the immediate cause of death. The coroner reported that the infant died from a lacerated spleen. The child had also tested positive for measles.
The Pennsylvania Department of Health continues to classify the case as a measles-associated death. It means measles was linked to the case through laboratory or epidemiological evidence, but it does not necessarily mean the virus was listed as the direct medical cause of death.
The state has released little information about the second death because of privacy concerns.
Another point is important when discussing the infant. Routine MMR vaccination does not begin at birth, so the child would not have been old enough to receive the first standard dose.
The Outbreak Is Growing Much Faster than It Was Earlier This Summer
On August 25, the state reported 393 cases across 28 counties. By 6 p.m. on August 26, the total had reached 424. Local reporting also confirmed the first Westmoreland County case and a new case in Butler County.
The increase follows an already sharp acceleration. The American Academy of Pediatrics reported last week that Pennsylvania had added 91 cases in a single week, helping drive a national increase of 211 cases.
Lancaster County remains the main center of transmission, but the appearance of cases in additional counties shows why health officials are treating the situation as a statewide problem rather than a local outbreak.
There Is a Real Risk of Wider Spread
A much larger outbreak is possible if transmission continues at the current pace.
Measles spreads through the air and is one of the most contagious human infections. The virus can remain infectious in an indoor space for up to two hours after an infected person has left. Symptoms can appear 7 to 21 days after exposure, according to Pennsylvania health guidance on measles, which means the official case count always reflects infections that began days or weeks earlier.
Recent exposure alerts show how easily the virus can reach people outside the household. Pennsylvania officials warned this month about possible exposure at a soccer camp at Millersville University and at a Whole Foods Market in Lancaster. Earlier alerts involved a courthouse and other public locations.
The start of the school year adds another concern. Schools create long periods of indoor contact, and some communities in Pennsylvania have vaccination rates below the level public health experts consider sufficient to prevent sustained measles transmission. The outbreak also comes shortly after a federal vaccine executive order targeting parts of the childhood immunization schedule, including future changes involving MMR vaccination.
Lancaster County Has a Major Vaccination Gap
Vaccination rates in Lancaster County have fallen substantially over the past decade.
Recent reporting based on state data puts MMR coverage among kindergarten students in the county at about 87.6%, down from 95.5% in 2017.
That gap is important because two doses of MMR provide about 97% protection against measles. High community coverage also limits the number of susceptible people the virus can reach.
Pennsylvania has responded by dramatically increasing vaccination efforts. Since the outbreak began in April, state teams have administered more than 4,100 MMR doses through 91 pop-up clinics. Another 40 clinics are planned.
More than 35,000 Pennsylvanians received an MMR vaccine in July, about 10,000 more than during a typical month, according to the state update on the expanded measles response.
The Next Few Weeks Will Show Whether Pennsylvania Can Contain It
If Pennsylvania continues adding close to 100 cases a week, the state could move rapidly toward several hundred additional infections before autumn. That outcome is not guaranteed. Vaccination campaigns, isolation of infected people and fast contact tracing can break transmission chains.
The problem is that measles moves quickly through groups with low immunity. New cases in additional counties show that Lancaster County is no longer the only place that needs attention.
For now, the most important number is 94. That is how many cases Pennsylvania added in one week.
If that number begins falling, the outbreak may be coming under control. If it keeps rising as schools reopen, Pennsylvania could be entering a much larger phase of the outbreak.
