Washington, D.C., October 7, 2026 (PAHO) – The Pan American Health Organization (PAHO) brought together surveillance, laboratory, and immunization teams from across the Region for a virtual seminar to analyze the 2026 respiratory virus season in the Southern Hemisphere. With the peak period now over, the meeting provided an opportunity to share surveillance findings and draw lessons for countries in the Northern Hemisphere in preparation for the 2026–2027 season.
The regional assessment indicates that the season was within expectations. According to Andrea Vicari, director of PAHO’s Infectious Threats Management Unit, robust sentinel surveillance made it possible to detect cases, standardize monitoring, and evaluate the impact of interventions.
Regional Presentations
According to surveillance data, hospitalizations due to severe acute respiratory infection (SARI) in Brazil and the Southern Cone were lower than in the two previous seasons. Influenza A(H3N2) predominated, while influenza B circulated earlier than usual in Brazil and Chile, with no changes in severity. In the Andean subregion, respiratory syncytial virus (RSV) accounted for the largest share. Outside the Southern Hemisphere, RSV is increasing in Central America and the Caribbean, and COVID-19 in North America.
Subclade K (J.2.4.1) accounts for 96% of the influenza A(H3N2) sequences published on GISAID, and its mutations led to an update of the diagnostic kits distributed to countries. This case demonstrates that sequencing is not an end in itself: its value lies in turning data into decisions, from diagnosis to vaccine composition.
In this regard, on September 25, the WHO established the vaccine composition for the 2027 season in the Southern Hemisphere and recommended the same formulation for the 2026–2027 season in the Northern Hemisphere. Among the inputs for this decision were the effectiveness studies from the regional REVELAC-i network, based on the countries’ SARI sentinel networks. Based on data from more than 27,000 hospitalized patients in six countries between March 1 and July 20, the preliminary effectiveness of the vaccine in preventing influenza-related hospitalizations was 37%: 32% against influenza A, 27% against A(H3N2), and 45% against influenza B. The estimate for the full season will be released in November.
Experiences in Peru and Chile
In Peru, the season began earlier than usual, and RSV surpassed influenza in terms of positivity rates. Compared to the same period in 2025, there were 21% more hospitalizations, 4% fewer intensive care admissions, and 38% fewer deaths. In the coming months, the effect of monoclonal antibodies against RSV in newborns and of vaccination for pregnant women, both of which were introduced this year, will be evaluated.
In Chile, the circulation of respiratory viruses began earlier than usual, driven by rhinoviruses, and influenza arrived later. It was the season with the lowest cumulative SARI burden among the last four analyzed. Influenza vaccination coverage reached 79.6% of the target population, with more than 7.9 million people immunized, and coverage for the monoclonal antibody against RSV reached 97.7%. Since its introduction in 2024, there have been no reported deaths from RSV in children under one year of age.
The seminar is part of the commitment by PAHO and Member States to review findings from each hemisphere twice a year, so that the experience of one hemisphere can contribute to the preparedness of the other.