The U.S. Centers for Disease Control and Prevention reported 2,104 confirmed measles cases in the United States in 2026 as of the June 18 weekly update (CDC-measles-update-2026-06-18), making this the largest annual measles outbreak in the United States in at least three decades. The 2026 total exceeds the previous modern-era record of 1,274 confirmed cases set in 2019.
The Pan American Health Organization (PAHO) announced this week that it is postponing its planned re-evaluation of U.S. individual measles elimination status, citing the sustained transmission observed in the U.S. and several other member states. Context: in November 2025, PAHO’s Regional Verification Commission had already announced that the Region of the Americas as a whole had lost its regional measles elimination status, primarily due to endemic transmission established in Canada. The deferred 2026 review concerns U.S. individual country status specifically. The WHO defines measles elimination as interruption of endemic transmission for ≥12 months. The U.S. has maintained individual-country elimination status since 2000, though the PAHO review process now classifies the U.S. as “sustained with major concerns.”
Outbreak characteristics
The 2026 cases are concentrated in communities with lower vaccination coverage, including several with documented vaccine hesitancy and organised exemption networks. Measles is caused by a paramyxovirus with a basic reproduction number (R₀) of 12–18, meaning herd immunity requires vaccination coverage above 95% to prevent outbreak spread. National MMR coverage has declined below 95% in some age cohorts and geographic areas.
The MMR (measles-mumps-rubella) vaccine is two-dose, with the first dose administered at 12–15 months and the second at 4–6 years. Two doses provide approximately 97% protection against measles. The vaccine has been in routine use in the United States since 1963 (original measles vaccine) and the combined MMR since 1971.
PAHO elimination re-evaluation postponed
PAHO’s decision to defer the U.S. individual country review reflects the sustained character of the 2026 U.S. outbreak. Measles spreads efficiently across national borders; sustained transmission in a large member state undermines elimination status across the region. The timing of the next re-evaluation has not been announced.
Correction (2026-06-19): Two errors corrected by post-publication fact-check. (1) The previous modern-era record was stated as 1,282 cases set in 2019; the official CDC final count for 2019 is 1,274 confirmed cases. (2) The article stated PAHO is “postponing its planned Americas-wide elimination re-evaluation” without noting that the Americas region had already lost its regional measles elimination status in November 2025 (due to endemic transmission established in Canada); what PAHO deferred is the review of U.S. and Mexico individual country elimination status, not a first-time regional assessment. The article has been updated throughout to reflect these distinctions.