The overall 2026 figures represent the highest number of US cases in a single year since a major resurgence of the highly contagious disease in the period from 1989 to 1991, with more than 55,000 infections and 123 deaths.
"Reaching this milestone is particularly striking because we are only in July, and measles cases are still being reported throughout the country," said William Moss, epidemiology professor at Johns Hopkins Bloomberg School of Public Health.
Young people, ranging from infants to age 19, made up 69 per cent of cases tracked through July 23, with children younger than five comprising one-fifth of those infected this year, the Centers for Disease Control and Prevention (CDC) said on Friday.
One-tenth of those younger than five who were infected ended up hospitalised, along with three per cent of those aged five to 19. Measles-related hospitalisations in 2026 stand at 151 so far.
Measles can be fatal in severe cases but no deaths have been reported from the disease since January.
By comparison, the US tally for all of 2025 was 2289 infections, or 29 fewer than in the first seven months this year. Last year's total included 243 hospitalisations and three deaths.
The virus infection, which typically causes symptoms such as fever, rash and respiratory issues, can be averted with a vaccine commonly given in the US for three childhood diseases - measles, mumps and rubella. It is considered 97 per cent effective after two doses.
A surge in measles cases during the past two years has coincided with a steady slump in MMR immunisation rates for children since the start of the COVID-19 pandemic.
Average US vaccination coverage among kindergarten children dropped in 2025 to 92.5 per cent, well below the level of 95 per cent considered necessary to achieve effective "herd" immunity needed to prevent the spread of the virus, the CDC said.
Many health officials have cited a public backlash to the government's pandemic response and blame US Health Secretary Robert F Kennedy Jr's anti-vaccine policies for further undermining trust in disease-preventing immunisations by embracing unproven theories about vaccine dangers.
Kennedy has repeatedly promoted the false claim that measles vaccines are linked to autism despite overwhelming scientific evidence to the contrary.
As much as 93 per cent of 2026's cases were in unvaccinated individuals, with a fraction of the rest having received one or two doses of vaccine before being infected, the CDC said.
Infections were documented by the CDC this year in 45 states and the District of Columbia, with 93 per cent associated with one of 35 new outbreaks reported in 2026, versus 48 in 2025.
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