The CDC reported 3,471 confirmed measles cases across the U.S. as of September 17, 2026 — up 177 cases, or about 5.4%, from the week before. It’s the highest annual measles total the country has seen in more than three decades.

Where cases are showing up

Cases have now been reported in 47 jurisdictions nationwide, with 17 additional cases among international visitors. Pennsylvania has seen the most severe outbreak, reporting its fourth measles-related death of the year. Health officials say 39 new outbreaks have started in 2026, and about 95% of this year’s cases — 3,296 of 3,471 — are linked to an outbreak rather than an isolated case.

Why cases climb when schools go back

Measles is one of the most contagious diseases known — a single infected person can spread it to 9 out of 10 unvaccinated people they come into close contact with. The return to school in September, combined with the start of respiratory virus season, tends to accelerate spread in communities with lower vaccination rates.

Symptoms to watch for

Symptoms typically appear 7 to 14 days after exposure and include a high fever that can spike above 104°F, cough, runny nose, and red, watery eyes, followed a few days later by the telltale rash. About 1 in 5 unvaccinated people who catch measles is hospitalized, and complications like pneumonia or brain swelling can be serious, particularly in young children.

Two doses of the MMR vaccine are about 97% effective at preventing infection. Pediatricians recommend the first dose at 12–15 months and the second at 4–6 years old. If you’re unsure of your own vaccination status or your child’s, a family doctor or local health department can check records or arrange a titer test.