Adjuvanted and high-dose influenza vaccines had comparable effectiveness against test-confirmed influenza outcomes including hospitalizations in overall and high-risk older adults in the 2022–2023 and 2023–2024 seasons

OBJECTIVES: Evaluate relative vaccine effectiveness (rVE) of adjuvanted quadrivalent influenza vaccine (aQIV) versus high-dose QIV (HD-QIV) in preventing test-confirmed influenza during 2023-2024 in any setting and emergency department (ED)/hospitalization settings, as well as in preventing hospitalizations in overall and high-risk older adults in a pooled analysis from 2022-2024. METHODS: This retrospective test-negative design study included US adults aged ≥65 years vaccinated with aQIV or HD-QIV who presented with acute respiratory or febrile illness and were tested for influenza per routine care. The rVE of aQIV versus HD-QIV was evaluated combining inverse probability of treatment weighting and logistic regression to adjust for potential confounders. RESULTS: The 2023-2024 season included 37,377 vaccinated and tested individuals (3,174 cases; 34,203 controls). rVE of aQIV versus HD-QIV was -0.9% (95% CI: -9.9, 7.3) in any setting and 0.5% (-12.1, 11.6) in ED/hospitalization settings. For pooled analyses of hospitalizations, rVE was -0.5% (-13.4, 10.9) overall and -1.3% (-14.4, 10.4) in the high-risk subgroup. CONCLUSIONS: aQIV and HD-QIV provided comparable protection for prevention of test-confirmed influenza among older adults in any and ED/hospitalization settings in the 2023-2024 season and for hospitalizations in overall and high-risk older adults in pooled 2022-2024 analyses.