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J Infect Dis . Vaccine Effectiveness Against Influenza A(H1N1), A(H3N2), and B-Associated Hospitalizations-United States, September 1, 2023-May 31,

tetano

Editor, Senior Moderator
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[SUP] 1 [/SUP], Elizabeth J Harker[SUP] 1 [/SUP], Seana Cleary[SUP] 1 [/SUP], Yuwei Zhu[SUP] 2 [/SUP], Carlos G Grijalva[SUP] 2 [/SUP], James D Chappell[SUP] 2 [/SUP], Jillian P Rhoads[SUP] 2 [/SUP], Adrienne Baughman[SUP] 2 [/SUP], Jonathan D Casey[SUP] 2 [/SUP], Paul W Blair[SUP] 2 [/SUP], Ian D Jones[SUP] 2 [/SUP], Cassandra A Johnson[SUP] 2 [/SUP], Natasha B Halasa[SUP] 2 [/SUP], Adam S Lauring[SUP] 3 [/SUP], Emily T Martin[SUP] 3 [/SUP], Manju Gaglani[SUP] 4 5 [/SUP], Shekhar Ghamande[SUP] 5 [/SUP], Cristie Columbus[SUP] 5 6 [/SUP], Jay S Steingrub[SUP] 7 [/SUP], Abhijit Duggal[SUP] 8 [/SUP], Jamie R Felzer[SUP] 9 [/SUP], Matthew E Prekker[SUP] 10 [/SUP], Ithan D Peltan[SUP] 11 12 [/SUP], Samuel M Brown[SUP] 11 12 [/SUP], David N Hager[SUP] 13 [/SUP], Michelle N Gong[SUP] 14 [/SUP], Amira Mohamed[SUP] 14 [/SUP], Matthew C Exline[SUP] 15 [/SUP], Akram Khan[SUP] 16 [/SUP], Samantha A N Ferguson[SUP] 17 [/SUP], Jarrod Mosier[SUP] 18 [/SUP], Nida Qadir[SUP] 19 [/SUP], Steven Y Chang[SUP] 19 [/SUP], Adit A Ginde[SUP] 20 [/SUP], Anne Zepeski[SUP] 21 [/SUP], Christopher Mallow[SUP] 22 [/SUP], Estelle S Harris[SUP] 11 [/SUP], Nicholas J Johnson[SUP] 23 [/SUP], Kevin W Gibbs[SUP] 24 [/SUP], Jennie H Kwon[SUP] 25 [/SUP], Ivana A Vaughn[SUP] 26 [/SUP], Mayur Ramesh[SUP] 26 [/SUP], Basmah Safdar[SUP] 27 [/SUP], Diya Surie[SUP] 28 [/SUP], Fatimah S Dawood[SUP] 28 [/SUP], Sascha Ellington[SUP] 1 [/SUP], Wesley H Self[SUP] 2 [/SUP]



Affiliations
Abstract

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.

 
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