US faces its worst measles year in over three decades amid vaccination decline

The United States reports its highest annual measles cases since 1991, driven by outbreaks linked to declining vaccination coverage and rising immunity gaps, prompting urgent calls for increased immunisation efforts.

The United States is facing its worst measles year in more than three decades, with the Centers for Disease Control and Prevention reporting 3,471 confirmed cases as of September 17. That is the highest annual total since 1991 and marks a sharp escalation from the summer, when the country had already overtaken last year’s tally. Reuters has previously reported that the surge has been driven largely by outbreaks rather than scattered cases, with the CDC saying 38 outbreaks have been recorded this year and that about 95% of infections are linked to them. Utah remains the largest active cluster, while Pennsylvania has become a newer area of concern. The public-health message from officials is increasingly blunt: vaccination is still the most effective way to slow transmission and protect children, adults and those who cannot be immunised for medical reasons.

The scale of the outbreak is being shaped by who is getting sick. CDC surveillance data show that roughly 93% of confirmed patients are unvaccinated or have unknown vaccination status, a pattern that has held throughout the year. The Associated Press reported in July that the United States had already recorded 2,318 cases by July 24, while Johns Hopkins’ International Vaccine Access Centre said the country had passed its full-year 2025 total just days earlier. That earlier milestone underscored how quickly the outbreak was accelerating. At the time, hospitalisation rates were lower than in 2025, but officials warned that the virus’s ability to spread in clusters of susceptible people meant the situation could worsen quickly if immunity gaps persisted.

Those gaps have widened as childhood vaccination rates have slipped. CDC figures cited in the article show kindergarten coverage for the measles, mumps and rubella vaccine falling from 95.2% in the 2019-20 school year to 92.4% in 2025-26, leaving an estimated 280,000 kindergartners without documented protection. Public-health researchers have warned that even small declines can have serious consequences: one study cited in the article estimated that a 1% drop in childhood MMR coverage could result in about 17,000 extra measles cases, 4,000 hospitalisations and 36 preventable deaths each year. The widening risk is why health experts continue to emphasise herd immunity, the community-level protection that helps shield infants too young for vaccination and people whose immune systems make vaccination unsafe.

Public-health advice remains consistent despite the outbreak’s growth. Two doses of the MMR vaccine provide the strongest protection, and the CDC says one dose is highly effective but not as protective as the full series. The standard schedule calls for the first dose at 12 to 15 months and the second at 4 to 6 years. Officials also advise families to check vaccination records, especially if they are unsure of their own immunity, and to speak with a healthcare provider before travel, including international trips. Infants as young as six months may need an earlier dose before leaving the country. Anyone with symptoms such as fever, cough, runny nose, red eyes or the characteristic rash should isolate and call ahead before seeking medical care, because measles can spread before many people realise what they have.

The concern now extends beyond the number of cases. Public-health specialists have warned that continued domestic spread, combined with travel-related exposure, could keep driving infections higher in the months ahead. The article notes that the United States risks losing the measles elimination status it has held since 2000 if outbreaks continue to expand. That possibility gives added weight to the current warning from health officials: the country’s best defence is still high vaccination coverage, especially in communities where exemptions, hesitancy and missed doses have left enough children and adults vulnerable for the virus to move rapidly.