Interim Effectiveness Estimates of 2025 Southern Hemisphere Influenza Vaccines in Preventing Influenza-Associated Outpatient and Hospitalized Illness — Eight Southern Hemisphere Countries, March–September 2025

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.

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Publication Details

Journal
MMWR Morbidity and Mortality Weekly Report
Published
2025-09-25
DOI
https://doi.org/10.15585/mmwr.mm7436a3
Citations
4
Primary Topic
Influenza Virus Research Studies
Type
article
Field-Weighted Citation Impact
5.42

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article

Interim Effectiveness Estimates of 2025 Southern Hemisphere Influenza Vaccines in Preventing Influenza-Associated Outpatient and Hospitalized Illness — Eight Southern Hemisphere Countries, March–September 2025

Natalia Vergara, Timothy J. Wood, Q. Sue Huang, Estefanía Benedetti et al.
4 citations
MMWR Morbidity and Mortality Weekly Report
Influenza Virus Research Studies
5.42
article

Interim Effectiveness Estimates of 2025 Southern Hemisphere Influenza Vaccines in Preventing Influenza-Associated Outpatient and Hospitalized Illness — Eight Southern Hemisphere Countries, March–September 2025

Natalia Vergara, Timothy J. Wood, Q. Sue Huang, Estefanía Benedetti, Annette K. Regan, Carla Voto, Sílvia Gómez, Francisco José de Paula Júnior, Savanah Russ, Francisco Nogareda, Allen Cheng, Nigel Stocks, Sheena G. Sullivan, Andrew T. Anglemyer, Marina Pasinovich, Anna N. Chard, Ana Catarina de Melo Araújo, P. Ferrari, Carlos Saavedra, Christopher C. Blyth, Nicole Wolter, Eduardo Azziz‐Baumgartner, Paula Couto, Walquíria Aparecida Ferreira de Almeida, Sibongile Walaza, Natalia Goñi, Rebecca Kondor, Monique Chilver, Rodrigo Fasce, Elena Penayo, Chavely Domínguez, Jenna Hassall, Jorge Jara, Eduardo Silvera, Phindi Zwane, Jeremy Tairovich
article en
4 citations

Abstract

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.

MMWR Morbidity and Mortality Weekly ReportVol. 74(36)
Bill and Melinda Gates Foundation, Pfizer, Sanofi, World Health Organization, Novavax, Moderna, EuroQol Research Foundation, Seqirus, National Institutes of Health, Centers for Disease Control and Prevention, Pan American Health Organization, National Center for Immunization and Respiratory Diseases
Openalex Percentile: Top 4%
Influenza Virus Research Studies
5.42
DOIOpen Access PDFOpenAlex
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