Situation Report #4: Measles in the Americas Region. 4 June 2026

 Between epidemiological week (EW) 1 and EW 21 of 2026 (ending on 30 May 2026), the Region of the Americas reported 21,431 confirmed measles cases from 17 countries and territories, including 31 deaths, representing a 234% increase compared to the same period in 2025. Mexico (11,184), Guatemala (6,655), the United States (1,983) and Canada (1,042) accounted for the majority (97%) of confirmed cases. 

During EW 19 and EW 20 of 2026, the Region of the Americas reported 1,040 new confirmed measles cases across nine countries and territories, representing a 16.2% decrease compared with the previous two-week period (EW17-18; 1,343 new cases). This decline was driven primarily by sustained reductions in the United Stated and continued decreases in Canada and Mexico. Peru was the main exception, with cases continuing to increase during this period, mostly concentrated in Puno. Trends in Guatemala should be interpreted with caution, given possible reporting delays or updates in recent weeks2. 

The outbreak continues to disproportionately affect young children, with the highest incidence rates observed among infants under one year of age. Approximately 85% of confirmed cases are either unvaccinated or have an unknown vaccination status. The D8 genotype, DSId 9171 has been identified across multiple countries and remains the main genotype detected in the Region. 

Model-based estimates of transmission as of EW 21 indicate continued declines in Mexico and Canada, sustained increases in Peru, and stabilizing dynamics in the United States, with the effective reproduction number (Rₜ) near 1. Full estimates and four-week forecasts are presented in Table 3. Nevertheless, sustained transmission could still occur through gradual, drop-by-drop spread, underscoring the need to continue strengthening vaccination efforts.