Health authorities in Uruguay, Argentina and Peru are preparing for potential measles spread tied to Pope Leo XIV’s mass gatherings as regional cases climb sharply in 2026.
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Pope Leo XIV’s Nov. 6-17 trip to South America has prompted health officials to heighten measles surveillance and vaccination efforts, citing surging cases and the risk that large religious gatherings could help the virus spread.
The Pan American Health Organization (PAHO) assessed the public health risk of measles in the context of the religious mass gatherings as “very high,” noting nearly a five-fold increase in cases between January and October compared with the same period in 2025.
Uruguay implemented a nationwide intensified surveillance monitoring period until Nov. 29, three weeks after Leo’s departure from the country, according to Nataly Rodriguez, director of epidemiology at Uruguay’s health ministry. Rodriguez said the health ministry has been emphasizing “the importance of keeping vaccination schedules up to date” as a preventive strategy.
Measles spreads easily through the air and can be contagious even before symptoms appear. PAHO’s description says the virus first infects the respiratory tract, then spreads through the body, typically causing high fever, runny nose, cough, red watery eyes and a rash. The vaccine is described as “extremely effective,” but the first of two doses is not usually recommended until a child’s first birthday.
To stop measles transmission in a community and protect infants and others who cannot get vaccinated, the evidence says at least 95% of the population must be fully vaccinated with two doses. As of 2025, only Uruguay had reached that threshold, while Peru reached 90% with one dose and 82% with two doses, and Argentina reached 84% with one dose and 55% with both doses.
PAHO reported 57,666 confirmed measles cases in 17 countries and territories in the Americas between January and the end of October, nearly five times the number recorded during the same period in 2025. At least 81 people have died so far this year due to measles, and Peru has identified 170 cases across five cities—Lima, Chiclayo, Cajamarca, Cusco and Pucallpa—where Leo will be visiting.
In Peru, PAHO said it supported vaccination initiatives targeting adolescents, strengthening vaccine storage and delivery capacity, intensifying vaccination along the border with Brazil, and carrying out campaigns in late October in areas with the highest rates of transmission. The campaigns included doses for babies aged six to 11 months and vaccination for people up to 29 years old. By the end of September, 1.2 million vaccine doses had been administered since April, with more than two million additional doses available.
In Argentina, officials issued a late-October warning about risk linked to the pope’s visit after estimating up to 4 million people in the province of Buenos Aires. The evidence also states that Argentina’s president, Javier Milei, slashed the healthcare budget, coinciding with a measles outbreak that led to Argentina’s first measles death in two decades in April 2025. Marcela Lopez Yunes, a pediatric infectious disease specialist, said she had not seen what she considered sufficient public communication to encourage vaccination and called for diseases like measles to receive more attention.
A spokesperson for Argentina’s health ministry said the federal government is responsible for purchasing and distributing vaccines, while provinces administer them, and that there is an ongoing public service announcement on the importance of vaccination in general.
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