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J Infect Dis
. 2025 Apr 8:jiaf185.
doi: 10.1093/infdis/jiaf185. Online ahead of print. Vaccine Effectiveness Against Influenza A(H1N1), A(H3N2), and B-Associated Hospitalizations-United States, September 1, 2023-May 31, 2024
Nathaniel M Lewis 1 , Elizabeth J Harker 1 , Seana Cleary 1 , Yuwei Zhu 2 , Carlos G Grijalva 2 , James D Chappell 2 , Jillian P Rhoads 2 , Adrienne Baughman 2 , Jonathan D Casey 2 , Paul W Blair 2 , Ian D Jones 2 , Cassandra A Johnson 2 , Natasha B Halasa 2 , Adam S Lauring 3 , Emily T Martin 3 , Manju Gaglani 4 5 , Shekhar Ghamande 5 , Cristie Columbus 5 6 , Jay S Steingrub 7 , Abhijit Duggal 8 , Jamie R Felzer 9 , Matthew E Prekker 10 , Ithan D Peltan 11 12 , Samuel M Brown 11 12 , David N Hager 13 , Michelle N Gong 14 , Amira Mohamed 14 , Matthew C Exline 15 , Akram Khan 16 , Samantha A N Ferguson 17 , Jarrod Mosier 18 , Nida Qadir 19 , Steven Y Chang 19 , Adit A Ginde 20 , Anne Zepeski 21 , Christopher Mallow 22 , Estelle S Harris 11 , Nicholas J Johnson 23 , Kevin W Gibbs 24 , Jennie H Kwon 25 , Ivana A Vaughn 26 , Mayur Ramesh 26 , Basmah Safdar 27 , Diya Surie 28 , Fatimah S Dawood 28 , Sascha Ellington 1 , Wesley H Self 2
Affiliations
Background: The 2023-2024 influenza season included sustained elevated activity from December 2023-February 2024 and continued activity through May 2024. Influenza A(H1N1), A(H3N2), and B viruses circulated during the season.
Methods: During September 1, 2023-May 31, 2024, a multistate sentinel surveillance network of 24 medical centers in 20 U.S. states enrolled adults aged ≥18 years hospitalized with acute respiratory illness (ARI). Consistent with a test-negative design, cases tested positive for influenza viruses by molecular or antigen test, and controls tested negative for influenza viruses and SARS-CoV-2. Vaccine effectiveness (VE) against influenza-associated hospitalization was calculated as (1 - adjusted odds ratio for vaccination) × 100%.
Results: Among 7690 patients, including 1170 influenza cases (33% vaccinated) and 6520 controls, VE was 40% (95% CI: 31%-48%) with varying estimates by age (18-49 years: 53% [34%-67%]; 50-64 years: 47% [31%-60%]; ≥65 years: 31% [16%-43%]). Protection was similar among immunocompetent patients (40% [30%-49%]) and immunocompromised patients (32% [7-50%]). VE was statistically significant against influenza B (67% [35%-84%]) and A(H1N1) (36% [21%-48%]) and crossed the null against A(H3N2) (19% [-8%-39%]). VE was higher for patients 14-60 days from vaccination (54% [40%-65%]) than >120 days (18% [-1%-33%]).
Conclusions: During 2023-2024, influenza vaccination reduced the risk of influenza A(H1N1)- and influenza B-associated hospitalizations among adults; effectiveness was lower in patients vaccinated >120 days prior to illness onset compared with those vaccinated 14-60 days prior.
Keywords: hospitalization; seasonal influenza; severe influenza; vaccine effectiveness; waning.
. 2025 Apr 8:jiaf185.
doi: 10.1093/infdis/jiaf185. Online ahead of print. Vaccine Effectiveness Against Influenza A(H1N1), A(H3N2), and B-Associated Hospitalizations-United States, September 1, 2023-May 31, 2024
Nathaniel M Lewis 1 , Elizabeth J Harker 1 , Seana Cleary 1 , Yuwei Zhu 2 , Carlos G Grijalva 2 , James D Chappell 2 , Jillian P Rhoads 2 , Adrienne Baughman 2 , Jonathan D Casey 2 , Paul W Blair 2 , Ian D Jones 2 , Cassandra A Johnson 2 , Natasha B Halasa 2 , Adam S Lauring 3 , Emily T Martin 3 , Manju Gaglani 4 5 , Shekhar Ghamande 5 , Cristie Columbus 5 6 , Jay S Steingrub 7 , Abhijit Duggal 8 , Jamie R Felzer 9 , Matthew E Prekker 10 , Ithan D Peltan 11 12 , Samuel M Brown 11 12 , David N Hager 13 , Michelle N Gong 14 , Amira Mohamed 14 , Matthew C Exline 15 , Akram Khan 16 , Samantha A N Ferguson 17 , Jarrod Mosier 18 , Nida Qadir 19 , Steven Y Chang 19 , Adit A Ginde 20 , Anne Zepeski 21 , Christopher Mallow 22 , Estelle S Harris 11 , Nicholas J Johnson 23 , Kevin W Gibbs 24 , Jennie H Kwon 25 , Ivana A Vaughn 26 , Mayur Ramesh 26 , Basmah Safdar 27 , Diya Surie 28 , Fatimah S Dawood 28 , Sascha Ellington 1 , Wesley H Self 2
Affiliations
- PMID: 40198276
- DOI: 10.1093/infdis/jiaf185
Background: The 2023-2024 influenza season included sustained elevated activity from December 2023-February 2024 and continued activity through May 2024. Influenza A(H1N1), A(H3N2), and B viruses circulated during the season.
Methods: During September 1, 2023-May 31, 2024, a multistate sentinel surveillance network of 24 medical centers in 20 U.S. states enrolled adults aged ≥18 years hospitalized with acute respiratory illness (ARI). Consistent with a test-negative design, cases tested positive for influenza viruses by molecular or antigen test, and controls tested negative for influenza viruses and SARS-CoV-2. Vaccine effectiveness (VE) against influenza-associated hospitalization was calculated as (1 - adjusted odds ratio for vaccination) × 100%.
Results: Among 7690 patients, including 1170 influenza cases (33% vaccinated) and 6520 controls, VE was 40% (95% CI: 31%-48%) with varying estimates by age (18-49 years: 53% [34%-67%]; 50-64 years: 47% [31%-60%]; ≥65 years: 31% [16%-43%]). Protection was similar among immunocompetent patients (40% [30%-49%]) and immunocompromised patients (32% [7-50%]). VE was statistically significant against influenza B (67% [35%-84%]) and A(H1N1) (36% [21%-48%]) and crossed the null against A(H3N2) (19% [-8%-39%]). VE was higher for patients 14-60 days from vaccination (54% [40%-65%]) than >120 days (18% [-1%-33%]).
Conclusions: During 2023-2024, influenza vaccination reduced the risk of influenza A(H1N1)- and influenza B-associated hospitalizations among adults; effectiveness was lower in patients vaccinated >120 days prior to illness onset compared with those vaccinated 14-60 days prior.
Keywords: hospitalization; seasonal influenza; severe influenza; vaccine effectiveness; waning.