The United States entered the week facing the likely loss of its measles elimination status, as a Pan American Health Organization (PAHO) commission prepared to begin a four-day review on Tuesday. US cases have reached their highest level in roughly 35 years. Public health specialists and state health departments said on Monday that the evidence of sustained spread made it difficult for the US to retain the designation.

The US has held elimination status since 2000. A country loses it when a single chain of transmission persists for 12 months or more. PAHO announced in March that its Measles and Rubella Elimination Regional Monitoring and Re-Verification Commission would assess the US in November during its regular annual meeting. Canada lost its status in November 2025, leaving the Americas without region-wide elimination.

The case surge began with the West Texas outbreak in January 2025. That outbreak killed two unvaccinated children and an unvaccinated adult in Texas and New Mexico. Large outbreaks followed in South Carolina's Upstate region and along the Utah–Arizona border. Data published by the Centers for Disease Control and Prevention showed annual case counts surpassing 2025's total, which had itself been the highest since 1991.

The central question for the commission is whether those outbreaks form one continuous chain or several separate introductions. The CDC under Health Secretary Robert F. Kennedy Jr has previously argued that genomic data did not prove a single unbroken chain.

The American Academy of Pediatrics has blamed falling childhood vaccination rates for the resurgence. CDC figures show kindergarten MMR coverage has slipped below the 95 per cent threshold needed for herd immunity.

Loss of status would carry no direct legal penalty. It would, however, mark a symbolic reversal for a country that led global elimination efforts. PAHO is expected to announce the commission's conclusions after the meeting ends on Friday. Paediatricians and state epidemiologists said the outcome could shape vaccination campaigns ahead of the winter travel season.