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Lancet Glob Health
. 2025 Feb;13(2):e203-e211.
doi: 10.1016/S2214-109X(24)00473-X. Effectiveness of 2023 southern hemisphere influenza vaccines against severe influenza-associated illness: pooled estimates from eight countries using the test-negative design
Radhika Gharpure 1 , Annette K Regan 2 , Francisco Nogareda 3 , Allen C Cheng 4 , Christopher C Blyth 5 , Siobhan St George 6 , Q Sue Huang 7 , Tim Wood 7 , Andrew Anglemyer 7 , Kriengkrai Prasert 8 , Prabda Praphasiri 9 , William W Davis 10 , Chakrarat Pittayawonganon 11 , Regina Ercole 12 , Analia Iturra 13 , Walquiria Aparecida Ferreira de Almeida 14 , Francisco José de Paula Júnior 14 , Marcela Avendaño Vigueras 15 , Maria Fernanda Olivares Barraza 16 , Chavely Domínguez 17 , Elena Penayo 17 , Natalia Goñi 18 , Daiana Tritten 19 , Paula Couto 3 , Daniel Salas 3 , Ashley L Fowlkes 1 , Lindsey M Duca 1 , Eduardo Azziz-Baumgartner 1 , Sheena G Sullivan 20
Affiliations
Background: Annual estimates of seasonal influenza vaccine effectiveness can guide global risk communication and vaccination strategies to mitigate influenza-associated illness. We aimed to evaluate vaccine effectiveness in countries using the 2023 southern hemisphere influenza vaccine formulation.
Methods: We evaluated end-of-season influenza vaccine effectiveness across eight countries (Argentina, Australia, Brazil, Chile, New Zealand, Paraguay, Thailand, and Uruguay) that used the 2023 southern hemisphere vaccine formulation, with use of a test-negative design. All patients who attended participating hospitals with severe acute respiratory illness were tested by RT-PCR for influenza. We calculated country-specific, network-specific, and pooled vaccine effectiveness against hospitalisation. For countries with sufficient data, we also calculated vaccine effectiveness against intensive care unit (ICU) admission by comparing the odds of vaccination among test-positive cases to that among test-negative controls. We evaluated vaccine effectiveness for groups prioritised for vaccination (young children aged 1-4 years, people aged 5-64 years with underlying health conditions, and older adults aged ≥65 years).
Findings: From March 5 to Nov 27, 2023, 31 368 individuals were admitted to hospital with severe acute respiratory infection in the eight included countries. Of these, 12 609 individuals admitted to hospital (6452 [51·2%] female and 6157 [48·8%] male) who met inclusion criteria and had complete data were included in the analysis, including 4388 test-positive cases and 8221 test-negative controls. Pooled vaccine effectiveness against hospitalisation with any influenza virus was 51·9% (95% CI 37·2-66·7), with substantial heterogeneity across countries (I2 74%). Vaccine effectiveness against ICU admission from any influenza virus was 67·7% (44·5-81·2) in Chile and 69·7% (45·3-83·3) in Australia. Vaccine effectiveness estimates against hospitalisation were highest for young children (70·9% [47·5-94·4]) and lowest for older adults (47·7% [24·9-70·5]).
Interpretation: Across eight countries, 2023 southern hemisphere vaccines were effective in reducing hospitalisations from influenza illness. Use of common protocols can facilitate data pooling to provide a comprehensive evaluation of vaccine effectiveness across settings.
Funding: US Centers for Disease Control and Prevention cooperative agreements to the Pan American Health Organization and the Thailand Ministry of Public Health; the Australian Government Department of Health and Aged Care; and the New Zealand Ministry of Health.
. 2025 Feb;13(2):e203-e211.
doi: 10.1016/S2214-109X(24)00473-X. Effectiveness of 2023 southern hemisphere influenza vaccines against severe influenza-associated illness: pooled estimates from eight countries using the test-negative design
Radhika Gharpure 1 , Annette K Regan 2 , Francisco Nogareda 3 , Allen C Cheng 4 , Christopher C Blyth 5 , Siobhan St George 6 , Q Sue Huang 7 , Tim Wood 7 , Andrew Anglemyer 7 , Kriengkrai Prasert 8 , Prabda Praphasiri 9 , William W Davis 10 , Chakrarat Pittayawonganon 11 , Regina Ercole 12 , Analia Iturra 13 , Walquiria Aparecida Ferreira de Almeida 14 , Francisco José de Paula Júnior 14 , Marcela Avendaño Vigueras 15 , Maria Fernanda Olivares Barraza 16 , Chavely Domínguez 17 , Elena Penayo 17 , Natalia Goñi 18 , Daiana Tritten 19 , Paula Couto 3 , Daniel Salas 3 , Ashley L Fowlkes 1 , Lindsey M Duca 1 , Eduardo Azziz-Baumgartner 1 , Sheena G Sullivan 20
Affiliations
- PMID: 39890222
- PMCID: PMC11783037
- DOI: 10.1016/S2214-109X(24)00473-X
Background: Annual estimates of seasonal influenza vaccine effectiveness can guide global risk communication and vaccination strategies to mitigate influenza-associated illness. We aimed to evaluate vaccine effectiveness in countries using the 2023 southern hemisphere influenza vaccine formulation.
Methods: We evaluated end-of-season influenza vaccine effectiveness across eight countries (Argentina, Australia, Brazil, Chile, New Zealand, Paraguay, Thailand, and Uruguay) that used the 2023 southern hemisphere vaccine formulation, with use of a test-negative design. All patients who attended participating hospitals with severe acute respiratory illness were tested by RT-PCR for influenza. We calculated country-specific, network-specific, and pooled vaccine effectiveness against hospitalisation. For countries with sufficient data, we also calculated vaccine effectiveness against intensive care unit (ICU) admission by comparing the odds of vaccination among test-positive cases to that among test-negative controls. We evaluated vaccine effectiveness for groups prioritised for vaccination (young children aged 1-4 years, people aged 5-64 years with underlying health conditions, and older adults aged ≥65 years).
Findings: From March 5 to Nov 27, 2023, 31 368 individuals were admitted to hospital with severe acute respiratory infection in the eight included countries. Of these, 12 609 individuals admitted to hospital (6452 [51·2%] female and 6157 [48·8%] male) who met inclusion criteria and had complete data were included in the analysis, including 4388 test-positive cases and 8221 test-negative controls. Pooled vaccine effectiveness against hospitalisation with any influenza virus was 51·9% (95% CI 37·2-66·7), with substantial heterogeneity across countries (I2 74%). Vaccine effectiveness against ICU admission from any influenza virus was 67·7% (44·5-81·2) in Chile and 69·7% (45·3-83·3) in Australia. Vaccine effectiveness estimates against hospitalisation were highest for young children (70·9% [47·5-94·4]) and lowest for older adults (47·7% [24·9-70·5]).
Interpretation: Across eight countries, 2023 southern hemisphere vaccines were effective in reducing hospitalisations from influenza illness. Use of common protocols can facilitate data pooling to provide a comprehensive evaluation of vaccine effectiveness across settings.
Funding: US Centers for Disease Control and Prevention cooperative agreements to the Pan American Health Organization and the Thailand Ministry of Public Health; the Australian Government Department of Health and Aged Care; and the New Zealand Ministry of Health.