A correspondence article published in The Lancet early this month reports that the US is facing its largest measles outbreak in decades, raising concerns that the country may be approaching a loss of measles elimination status.
The US had 2,288 confirmed measles cases across 45 states in 2025—the most annual cases of measles since 1991—and has reported 1,952 cases so far in 2026, many of which stem from outbreaks that began in 2025.
According to the article, the outbreak began in Texas in January 2025 following two imported cases and has since expanded through sustained local transmission. The findings are based on routinely reported public health surveillance data and apply established U.S. Centers for Disease Control and Prevention (CDC) elimination indicators to assess whether endemic transmission is re-emerging.
Measles elimination in the US, achieved in 2000, requires the absence of continuous endemic transmission for at least one year. According to the article authors, “four of seven indicators of sustained measles elimination status have already been missed, and the remaining three indicators are unlikely to be achieved,” pending further epidemiological and genomic review.
Sustained transmission signals
Across 53 documented outbreaks, 94% of cases were attributed to local transmission rather than importation. Genetic sequencing further indicated that most cases shared a dominant viral genotype, supporting evidence of ongoing domestic spread, the authors noted.
The analysis also reports that the effective reproduction number (Rt) remained above 1.0 for most of the outbreak period between January 2025 and February 2026, indicating sustained transmission. Although recent estimates show Rt falling below 1.0, the authors caution that model projections suggest case numbers could rise again ahead of the 2026 regional elimination status review.
Vaccination coverage is identified as a key contributing factor.
Kindergarten immunization rates for the 2024–2025 school year are reported to have fallen below the 95% herd immunity threshold, with some community-level estimates previously ranging between 79% and 89%. The authors also point to disruptions in routine immunization and increased vaccine hesitancy following the COVID-19 pandemic.
“Given the current epidemiological context, it appears highly likely that the USA will lose its measles elimination status in 2026,” conclude the authors. “Strengthening vaccination efforts, reducing exemption rates, and interrupting ongoing local transmission will be essential to reverse this trajectory.”
This article was created with the assistance of Generative AI and has undergone editorial review before publishing.
Note: This article was updated on May 22, 2026, with the latest CDC data on measles cases and outbreaks in the US.
