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Background Influenza vaccine efficacy/effectiveness can vary from season to season due in part to the dominant circulating strains and antigenic matching. This study reviews the relative vaccine efficacy/effectiveness (rVE) of high-dose inactivated trivalent influenza vaccine (HD-IIV3) compared with standard-dose influenza vaccines (SD-IIV3) in adults ≥65 years against influenza-associated outcomes across all influenza seasons, during seasons where A/H3N2 or A/H1N1 strains predominantly circulated, and where there was an antigenic match or mismatch of the vaccine and circulating strains. Methods A systematic review was conducted for studies assessing the rVE of HD-IIV3 against probable/laboratory-confirmed influenza-like illness (ILI), hospital admissions, and death in adults ≥65 years. Results from individual seasons were extracted from the identified studies, and surveillance data from each season were used to determine the dominant circulating strains and antigenic match. Results were then stratified based on clinical outcomes and seasonal characteristics and meta-analyzed to estimate pooled rVEs of HD-IIV3. Results 11 studies were meta-analyzed after screening 1,018 studies, providing data on 9 consecutive influenza seasons and over 12 million individuals receiving HD-IIV3. Across all influenza seasons, HD-IIV3 demonstrated improved protection against ILI compared with SD-IIV3 (rVE = 15.9%, 95% CI: 4.1–26.3%). HD-IIV3 was also more effective at preventing hospital admissions from all-causes (rVE = 8.4%, 95% CI: 5.7–11.0%), as well as influenza (rVE = 16.1%, 95% CI: 7.4–24.1%), pneumonia (rVE = 27.3%, 95% CI: 15.3–37.6%), pneumonia/influenza (rVE = 13.4%, 95% CI: 7.3–19.2%) and cardiorespiratory events (rVE = 17.9%, 95% CI: 15.0–20.8%). Some numerical differences were observed in the pooled rVE of outcomes in matched and mismatched seasons and in seasons where A/H3N2 or A/H1N1 strains were predominantly circulating (Table 1). Conclusion Evidence over 9 influenza seasons suggest that HD-IIV3 is consistently more effective than SD-IIV3 at reducing the clinical outcomes associated with influenza infection irrespective of circulating strain and antigenic match. This study was funded by sanofi pasteur. Disclosures All authors: No reported disclosures.

open forum infectious diseases

2745. Efficacy and Effectiveness of High-Dose Influenza Vaccine for Older Adults by Circulating Strain and Antigenic Match: A Systematic Review and Meta-Analysis