Effectiveness of Influenza Vaccines and Duration of Protection Against Hospitalisation During the 2024/25 Season in Northern Ireland, UK.

Authors

Magda Bucholc, Siobhán Murphy, Mark G O'Doherty, Suzanne Wilton, Emma Dickson, Declan T Bradley

Published in

Influenza and other respiratory viruses. Volume 20. Issue 8. Pages e70303.

Abstract

Seasonal influenza causes substantial morbidity and hospitalisation each year. We estimated influenza vaccine effectiveness (VE) against laboratory-confirmed influenza-associated hospitalisation among patients in Northern Ireland (NI) during the 2024/25 influenza season.
We used a test-negative design to estimate VE against hospitalisation. Influenza-positive cases and test-negative controls were identified through the national laboratory surveillance system and linked to hospital admission and vaccination records. VE was estimated by influenza type/subtype, age group, sex, vaccine type and time since vaccination.
Among 15,133 hospitalised patients, 2024 (13.4%) tested positive for influenza. Among the 2024 patients admitted with laboratory-confirmed influenza, the vast majority tested positive for influenza A (n = 1803; 89.1%), whereas 221 cases (10.9%) were influenza B. Subtyping of influenza A identified 606 A(H1) infections and 93 A(H3) infections; the remaining 1104 influenza A samples were not subtyped. VE against laboratory-confirmed influenza infection was 46.0% (95% CI: 39.7% to 51.8%), with higher VE in children aged 2-17 years (60.8%; 95% CI: 48.3% to 70.5%) than in adults aged 18-64 years (40.5%; 95% CI: 24.9% to 53.2%) and ≥ 65 years (42.3%; 95% CI: 33.2% to 50.1%). VE against influenza A across all ages was 41.4% (95% CI: 34.2% to 47.9%). Vaccination reduced the odds of hospitalisation due to influenza A(H1) by 44.3% (95% CI: 33.2% to 53.7%) and A(H3) by 49.9% (95% CI: 20.3% to 69.3%). VE against influenza B was higher at 76.4% (95% CI: 64.9% to 84.7%). For influenza A, VE was highest 2-8 weeks after vaccination at 51.9% (95% CI: 42.1% to 60.1%) and declined with time since vaccination to 44.6% (95% CI: 35.6% to 52.5%) at 9-16 weeks and 41.4% (95% CI: 15.4% to 60.1%) at ≥ 16 weeks. VE against influenza B remained high throughout the season. No statistically significant differences in VE by vaccine type were found.
Influenza vaccination reduced the risk of hospitalisation with laboratory-confirmed influenza during the 2024/25 season, offering meaningful protection at individual and population levels, with the greatest benefit observed in children.

PMID:
42560010
Bibliographic data and abstract were imported from PubMed on 06 Aug 2026.

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