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MMWR Morb Mortal Wkly Rep
. 2025 Sep 25;74(36):570-578.
doi: 10.15585/mmwr.mm7436a3.
Interim Effectiveness Estimates of 2025 Southern Hemisphere Influenza Vaccines in Preventing Influenza-Associated Outpatient and Hospitalized Illness - Eight Southern Hemisphere Countries, March-September 2025
Savanah Russ, Francisco Nogareda, Annette K Regan, Estefanía Benedetti, Marina Pasinovich, Carla Voto, Monique Chilver, Nigel Stocks, Sheena G Sullivan, Allen C Cheng, Christopher C Blyth, Jenna Hassall, Walquiria Aparecida Ferreira de Almeida, Francisco José de Paula Júnior, Ana Catarina de Melo Araújo, Natalia Vergara, Paula Camila Rodríguez Ferrari, Rodrigo A Fasce, Christian Saavedra, Elena Penayo, Silvia Gómez, Chavely Domínguez, Andrew Anglemyer, Tim Wood, Q Sue Huang, Sibongile Walaza, Phindi Zwane, Nicole Wolter, Natalia Goñi, Jeremy Tairovich, Eduardo Silvera, Paula Couto, Jorge Jara, Rebecca J Kondor, Eduardo Azziz-Baumgartner, Anna N Chard
Seasonal influenza vaccination provides important protection from influenza illness and associated potential complications. Monitoring seasonal influenza vaccine effectiveness (VE) in Southern Hemisphere countries can apprise health authorities in Northern Hemisphere countries about the potential protection provided from vaccination. Using data from influenza-like illness (ILI) and severe acute respiratory infection (SARI) sentinel surveillance networks in eight Southern Hemisphere countries, investigators estimated interim VE against influenza-associated outpatient visits and hospitalization using a test-negative case-control study design. During March-September 2025, Australia and South Africa identified 2,122 patients with ILI; Argentina, Australia, Brazil, Chile, New Zealand, Paraguay, and Uruguay identified 42,752 patients with SARI. Overall, 21.3% of patients with ILI and 15.9% of patients with SARI were vaccinated against influenza. Adjusted VE against influenza-associated outpatient visits and hospitalization was 50.4% and 49.7%, respectively, for any influenza virus, and 45.4% and 46.1%, respectively, for influenza A viruses. Adjusted VE against hospitalization with the predominant influenza subtype, A(H1N1)pdm09, was 41.6%. These interim estimates suggest that vaccination reduced medically attended influenza-associated illness by approximately one half in eight Southern Hemisphere countries. Health authorities should prioritize vaccination of all eligible persons ≥6 months to reduce incidence of influenza disease.
. 2025 Sep 25;74(36):570-578.
doi: 10.15585/mmwr.mm7436a3.
Interim Effectiveness Estimates of 2025 Southern Hemisphere Influenza Vaccines in Preventing Influenza-Associated Outpatient and Hospitalized Illness - Eight Southern Hemisphere Countries, March-September 2025
Savanah Russ, Francisco Nogareda, Annette K Regan, Estefanía Benedetti, Marina Pasinovich, Carla Voto, Monique Chilver, Nigel Stocks, Sheena G Sullivan, Allen C Cheng, Christopher C Blyth, Jenna Hassall, Walquiria Aparecida Ferreira de Almeida, Francisco José de Paula Júnior, Ana Catarina de Melo Araújo, Natalia Vergara, Paula Camila Rodríguez Ferrari, Rodrigo A Fasce, Christian Saavedra, Elena Penayo, Silvia Gómez, Chavely Domínguez, Andrew Anglemyer, Tim Wood, Q Sue Huang, Sibongile Walaza, Phindi Zwane, Nicole Wolter, Natalia Goñi, Jeremy Tairovich, Eduardo Silvera, Paula Couto, Jorge Jara, Rebecca J Kondor, Eduardo Azziz-Baumgartner, Anna N Chard
- PMID: 40996960
- PMCID: PMC12463193
- DOI: 10.15585/mmwr.mm7436a3
Seasonal influenza vaccination provides important protection from influenza illness and associated potential complications. Monitoring seasonal influenza vaccine effectiveness (VE) in Southern Hemisphere countries can apprise health authorities in Northern Hemisphere countries about the potential protection provided from vaccination. Using data from influenza-like illness (ILI) and severe acute respiratory infection (SARI) sentinel surveillance networks in eight Southern Hemisphere countries, investigators estimated interim VE against influenza-associated outpatient visits and hospitalization using a test-negative case-control study design. During March-September 2025, Australia and South Africa identified 2,122 patients with ILI; Argentina, Australia, Brazil, Chile, New Zealand, Paraguay, and Uruguay identified 42,752 patients with SARI. Overall, 21.3% of patients with ILI and 15.9% of patients with SARI were vaccinated against influenza. Adjusted VE against influenza-associated outpatient visits and hospitalization was 50.4% and 49.7%, respectively, for any influenza virus, and 45.4% and 46.1%, respectively, for influenza A viruses. Adjusted VE against hospitalization with the predominant influenza subtype, A(H1N1)pdm09, was 41.6%. These interim estimates suggest that vaccination reduced medically attended influenza-associated illness by approximately one half in eight Southern Hemisphere countries. Health authorities should prioritize vaccination of all eligible persons ≥6 months to reduce incidence of influenza disease.