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Incremental Benefit of High-Dose Compared to Standard-Dose Vaccine in Reducing Influenza Hospitalizations
23 Pages Posted: 22 May 2024
More...Abstract
Background: Annual vaccination is the primary medical intervention to prevent influenza and its complications. The US CDC recommends that patients above 65 receive the Fluzone high-dose (HD) quadrivalent vaccine due to their higher rates of severe events and reduced immune response. However, evidence regarding the HD vaccine's relative vaccine effectiveness (rVE) and absolute benefit in reducing hospitalizations due to influenza compared to the standard dose (SD) vaccine is warranted.
Methods: This retrospective cohort study included all members of Clalit Health Services, age 65, vaccinated with the HD or SD vaccine. The primary outcome was hospitalization with a primary or secondary diagnosis of influenza. We estimated the rVE and number needed to vaccinate (NNV) of the HD vaccine while adjusting for demographic factors and co-existing illnesses.
Results: Among the 418,603 and 393,125 members who met eligibility criteria during the 2022-2023 and 2023-2024 influenza seasons, respectively, 8,728 received the HD vaccine in 2022-2023 and 8,063 received it in 2023-2024. The primary outcome occurred in 18 cases (0·21%) in the HD vaccine group in 2022-2023 and in 27 cases (0·33%) in 2023-2024. The adjusted relative vaccine effectiveness was 27% (95% CI: -12% to 61%) for 2022-2023 and 7% (95% CI: -36% to 42%) for 2023-2024. The number needed to vaccinate with the HD vaccine to prevent one outcome event was 2,269 (95% CI: 1,004 to ∞) in 2022-2023 and 7,662 (95% CI: 1,293 to ∞) in 2023-2024. For a subgroup at the highest risk of hospitalization, the NNV was 1,289 (95% CI: 571 to ∞) in 2022-2023 and 4,719 (95% CI: 797 to ∞) in 2023-2024.
Interpretation: The HD vaccine does not offer a significant benefit over the SD vaccine, even among those elderly aged 65 and above with the highest risk of complications.
Funding: This research was partially supported by the European Research Council (ERC) project #949850 and the Israel Science Foundation (ISF), grant No. 3409/19, within the Israel Precision Medicine Partnership program.
Declaration of Interest: The authors declare no competing interests.
Ethical Approval: As the retrospective data was pseudonymized, the institutional Helsinki review board and data utilization committee approved using the retrospective cohort data without requiring specific consent from the members of Clalit Health Services (protocol number 0139-21-CHS).
Keywords: High dose vaccine, influenza, influenza vaccine, vaccine effectiveness
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