Measles is surging across the Americas as Pope Leo XIV’s Nov. 6–17, 2026, South America visit draws large crowds; the Pan American Health Organization (PAHO) rated the risk of spread around the gatherings “very high.”

From January through October 2026, PAHO recorded 57,666 confirmed cases across 17 countries and territories—nearly five times the total for the same period in 2025—with at least 81 deaths.

Measles spreads through the air and can infect others before symptoms appear, leaving infants especially vulnerable because the first vaccine dose is generally not recommended until age one; at least 95% of a community needs two-dose coverage to prevent sustained spread.

Vaccination coverage across the region remains uneven: Uruguay was the only country to meet the 95% two-dose threshold in 2025, compared with 82% in Peru and 55% in Argentina.

Peru has reported nearly 3,000 cases, the fourth-highest total in the Americas, including 170 in the five cities Leo plans to visit; authorities have expanded vaccination to babies aged six to 11 months and people up to age 29, administering 1.2 million doses since April and making more than two million additional doses available.

Argentina warned in late October that crowds of up to four million people could gather in Buenos Aires province, raising concern amid low vaccination coverage and criticism that public communication promoting vaccination is insufficient.

Concerns about Argentina’s preparedness have also focused on cuts under President Javier Milei that reduced the healthcare budget and affected agencies involved in immunization planning and monitoring; Leo criticized the austerity measures during his visit.

Argentina’s health ministry said the federal government buys and distributes vaccines, while provinces administer them, and noted that a public-service announcement promoting vaccination is underway.

Uruguay has stepped up vaccination efforts and extended nationwide measles surveillance through Nov. 29, three weeks after Leo’s departure.