U.S. Measles Cases Hit 4,852 in 2026, More Than Double Last Year, as Pennsylvania Outbreak Spreads

U.S. measles cases reached 4,852 confirmed infections in 2026 as of Oct. 29, according to the Centers for Disease Control and Prevention, more than double the 2,289 cases reported in all of 2025 and the highest annual count in decades. The surge is being driven by a months-long outbreak in Pennsylvania, where state health officials have now confirmed more than 1,300 cases and five deaths.

Cases have been reported in 47 jurisdictions, including Massachusetts, according to the CDC. Here is where the numbers stand, what is driving them and what health officials say people should do.

The national picture

The CDC counts 43 new measles outbreaks in 2026, defined as three or more related cases, and says 96% of this year’s cases are linked to an outbreak. The vaccination status of 96% of people who caught measles this year was listed as unvaccinated or unknown, NPR reported, citing CDC data. The agency’s own tally counts three confirmed measles deaths nationally; Pennsylvania alone reports five measles-associated deaths, because states confirm and report deaths on their own schedules and under their own case definitions.

The growth has not slowed. The CDC count stood at more than 4,580 on Oct. 22, according to NPR, so roughly 270 new cases were added in a single week.

By the numbers: how 2026 compares

By The Boston Report’s calculations from CDC figures, the 2026 total so far is about 2.1 times the full-year 2025 count, about 17 times the 285 cases of 2024, and about 3.8 times 2019, when 1,274 cases nearly cost the United States its measles elimination status. In 2020 the country recorded just 13 cases. Pennsylvania’s 1,338 cases as of late October account for roughly 28% of all U.S. cases this year.

The underlying trend is vaccination. Two doses of the measles, mumps and rubella (MMR) vaccine are about 97% effective at preventing measles, and one dose is about 93% effective, according to the CDC. CDC data show kindergarten MMR coverage nationwide fell from 95.2% in the 2019-20 school year, the level public health experts consider needed to block community spread, to 92.4% in 2025-26, leaving roughly 280,000 kindergartners without documented protection.

Pennsylvania’s outbreak

The Pennsylvania Department of Health reported 1,338 confirmed cases in 44 counties on Oct. 23, NPR reported, with 21 new cases as of Oct. 21, more than 250 hospitalizations and five deaths. Three of the people who died lived in Lancaster County. Lancaster and Mifflin counties, home to Amish communities with low vaccination rates, have been hit hardest. In an earlier update, when the count stood at 1,222 cases in 42 counties, the department said only four cases, less than 1%, were in vaccinated people.

Demand for shots has jumped. More than 39,000 measles vaccines were given in Pennsylvania during the first three weeks of October, compared with a typical 25,000 a month, the health department said. That is roughly 1.6 times a normal month’s volume in three weeks. Health Secretary Dr. Debra Bogen held a roundtable with Mifflin County health care providers last week. “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.

Other states: New York, Utah and South Carolina

New York Gov. Kathy Hochul declared a disaster emergency earlier in October, and the state had more than 160 confirmed cases as of Oct. 20, according to NPR. Utah has recorded more than 700 cases this year but had gone three weeks without a new diagnosis as of Oct. 20. South Carolina reported at least 997 cases in an outbreak that ended in April.

What to do

Health officials say the best protection is two doses of MMR vaccine. Adults who are unsure of their status can check vaccination records with a doctor or a state immunization registry, and a blood test can confirm immunity. Measles spreads through the air and can linger in a room for up to two hours after an infected person leaves, so anyone with a fever and rash who may have been exposed should call a doctor or clinic before showing up in person.

For more health coverage, see our report on the Ebola outbreak passing 10,000 cases and Boston research including Mass General’s federally funded Alzheimer’s platform trial.

Sources

• CDC: Measles Cases and Outbreaks
• NPR: U.S. measles cases more than double what they were last year as outbreak spreads (Oct. 25, 2026)
• Pennsylvania Department of Health: Statewide update on measles outbreak