A sign is posted outside a Pennsylvania Department of Health measles vaccination clinic located in Lancaster County in Peach Bottom, Pa., Tuesday, Oct. 20, 2026. Matt Rourke/AP hide caption

Matt Rourke/AP

The U.S. is grappling with its worst resurgence of measles in decades, with cases particularly high in the state of Pennsylvania.

New data from the U.S. Centers for Disease Control and Prevention shows there have been more than 4,580 measles cases across the U.S. since Oct. 22, which is more than double the number for the whole of 2025.

The vaccination status of 96% of those who contracted measles in 2026 was "Unvaccinated or Unknown," according to data from the CDC.

A measles outbreak across Pennsylvania has grown as officials urge residents to get fully vaccinated against the disease.

At least 1,338 cases of measles have been confirmed in 44 counties across the state so far this year, according to the Pennsylvania Department of Health on Friday. There were 21 new measles cases as of Oct. 21. More than 250 people have been hospitalized and 5 people have died, the department also said.

In Lancaster and Mifflin counties, two of the counties with the highest number of cases, local Amish communities, which have low vaccination rates, are being impacted the most. Of the five who have died, three lived in Lancaster County

On Thursday, Pennsylvania Secretary of Health Dr. Debra Bogen held a roundtable with Mifflin County healthcare providers to assess their needs in combatting the disease.

"Our state metrics and data tell part of the story of the measles outbreak in Pennsylvania, but listening to the people on the ground caring for people in affected communities like Mifflin County is essential to refining our public health response," Bogen said in a statement.

One of the best ways to protect oneself from getting the measles is vaccination, according to health officials. Two doses of measles, mumps, and rubella vaccine known as MMR, is nearly 97% effective against measles, according to the CDC. One dose is about 93% effective.

In Pennsylvania, the health department said healthcare providers have seen more residents interested in getting vaccinated for measles. Across the state, more than 39,000 measles vaccines were administered during the first three weeks of October – higher than an average of 25,000 vaccines administered across the state in one month, the health department said.

Earlier this month, New York Gov. Kathy Hochul declared a disaster emergency after rising measles cases. There have been over 160 confirmed measles across the state, according to Oct. 20 data from the New York State Department of Health.

Utah has also experienced a high number of measles cases. More than 700 people in Utah have been diagnosed with measles this year, according to Oct. 20 data from the Utah Department of Health and Human Services. There have not been any measles diagnoses in the state in 3 weeks, according to the department.

In South Carolina, which was dealing with an outbreak earlier this year, there have been at least 997 measles cases in 2026, according to the South Carolina Department of Public Health. The outbreak ended in April.