The United States has reported 2,371 confirmed measles cases in 2026 as of July 30. That is the highest yearly total since 1991, and it already beats the 2,289 cases recorded for all of 2025. The CDC confirmed the numbers on July 31, and the year is only half over.

The 2026 count includes 2,355 cases across 45 states and territories and 16 among international visitors. The CDC considers three or more related cases an "outbreak." Thirty-seven new outbreaks have been reported this year, and 94% of cases (2,219 of 2,371) are tied to these outbreaks. Of those, 846 come from outbreaks that started in 2026 and 1,373 from outbreaks that began in 2025, meaning many transmission chains from last year never stopped (CDC).

The numbers have been climbing fast. By July 22, the CDC had announced 58 new cases, bringing the total to 2,318. Just eight days later, 53 more cases were added. In 2025, the US saw 48 outbreaks and 2,289 cases. The year before that, 2024, had just 16 outbreaks and 285 cases. The jump from 2024 to 2025 was already large, and 2026 has now surpassed that (CIDRAP; US News).

The age breakdown of 2026 cases shows 469 (20%) in children under five, 1,161 (49%) in people aged 5 to 19, and 734 (31%) in adults 20 and older. Hospitalization rates show how serious the disease can be for the youngest patients: 10% of under-five cases were hospitalized, compared with 3% of those 5 to 19 and 10% of adults. In 2025, the rates were higher across all groups: 18% for under-fives, 6% for the 5-to-19 group, and 12% for adults (CDC).

Vaccination status is the clearest factor. In both 2025 and 2026, 93% of confirmed cases were in people who were unvaccinated or whose vaccination status was unknown. Three percent had received one dose of the MMR vaccine (which protects against measles, mumps, and rubella), and 4% had received the two doses that doctors recommend. The pattern is the same across both years, pointing to the same root cause: communities where vaccination rates have dropped.

Delaware shows how this works in practice. In July, the state reported its first measles case in more than a decade. Two days later, officials declared an outbreak with five cases. Delaware's kindergarten MMR vaccination rate fell from 98.5% in 2016 to 94.1% now, dipping below the roughly 95% threshold that experts say is needed for herd immunity. Herd immunity means enough people are vaccinated that the virus cannot easily spread, which also protects those who cannot get the shot for medical reasons. William Chasanov, an infectious disease doctor at Beebe Healthcare in Lewes, Delaware, and Robert Rosenbaum, the state's medical director for emergency medical services and preparedness, have been part of the response (The Guardian).

The federal response has drawn criticism. Robert F. Kennedy Jr., now serving as US health secretary, has falsely claimed it is "very difficult" for healthy children to die of measles. That claim goes against medical evidence: measles can cause pneumonia, brain inflammation, and death, especially in young children, even when they have no other health problems. The CDC's 2026 data shows that 49 children under five were hospitalized with measles this year, which fits with what doctors know about how severe the disease can be (The Guardian; New York Times).

The broader picture is one of falling vaccination rates meeting a virus that spreads extremely easily. Measles is so contagious that one sick person can infect up to 18 people who are not immune. That is why the 95% vaccination threshold matters so much: even a small drop below it opens the door to outbreaks. Delaware's drop of about 4.4 percentage points over a decade may sound minor, but it is the difference between the virus being blocked and the virus spreading. The fact that 45 jurisdictions have reported cases in 2026 tells us this is not limited to a few isolated communities.

The carryover of 1,373 cases from outbreaks that started in 2025 is also worth paying attention to. It means the virus kept spreading in chains that were never fully stopped, and each new person who is not vaccinated adds fuel to the fire. With 37 new outbreaks already declared in 2026 and months still to go, the case count will almost certainly keep rising.

Historical data from Our World in Data, which tracks US measles cases from 1919 to 2026, puts the current surge in perspective. The 2,371 cases so far this year are a tiny fraction of the hundreds of thousands reported each year before a vaccine existed. But the turnaround is sharp compared with recent decades, and the speed matters. When vaccination rates fall, measles comes back first in communities with the lowest coverage, then spreads through everyday social contact. Delaware went a decade without a single case and then had five in a matter of days. That is how fast it can happen (Our World in Data).