Relative Vaccine Effectiveness Of Adjuvanted Trivalent Influenza Vaccine Compared To Egg-Based Trivalent High Dose And Other Egg-Based Vaccines

Background: Influenza vaccine is the dominant strategy for prevention of disease and influenza-related hospitalization, especially in those over 65 years of age. Adjuvanted influenza vaccines offer the potential to increase effectiveness compared to alternative formulations. This study evaluated the relative vaccine effectiveness (rVE) of adjuvanted trivalent influenza vaccine (aTIV) compared to egg-based high-dose trivalent (TIV-HD), egg-based quadrivalent vaccine (QIVe), or egg-based standard-dose trivalent vaccine (TIVe-SD) against influenza-related hospitalizations and emergency room (ER) visits and office-visits among individuals 65 years of age and older during the 2017–2018 influenza season. Methods and materials: A retrospective cohort analysis was conducted among subjects 65 years of age and older vaccinated with one of four influenza vaccines (aTIV, TIV-HD, QIVe or TIVe-SD) to determine the relative effectiveness (rVE) against clinically-relevant outcomes. Professional fee, prescription claims and hospital charge master data in the U.S. provided the data to calculate event rates. The analysis adjusted for baseline characteristics – age group, gender, payer type, region, Charlson Comorbidity Index, month of flu vaccination, indicators of frail health status and pre-index hospitalization. The adjusted number of events and rates (per 1000 vaccinated subject-seasons) of influenza-related hospitalizations/ER visits and office visits and serious respiratory hospitalization encounters were calculated using inverse probability of treatment weighting (IPTW) and Poisson regressions. Results: During 2017–2018 flu season, 234,313 recipients of aTIV, 1,269,855 of TIV-HD, 212,287 of QIVe, and 106,491 of TIVe-SD were identified. Results differed by outcome. Following IPTW-adjustments for differences in baseline characteristics and Poisson regression, aTIV was significantly more effective in reducing influenza-related office visits and other respiratory events compared to all three other egg-based influenza vaccines. In contrast, aTIV was statistically comparable to TIV-HD (3.3% 95%CI: −2.7% to 8.9%) for prevention of influenza-related hospitalizations/ER visits and other relevant outcomes. aTIV was more effective than QIVe (8.6% 95%CI: 1.2–15.6%) and TIVe-SD (11.2% 95%CI: 2.3–19.4%) for prevention of influenza-related hospitalizations/ER visits. Conclusion: In the 2017–2018 season, adjusted analyses of aTIV and TIV-HD demonstrated comparable reductions in influenza-related hospitalizations/ER visits. aTIV demonstrated greater reductions in influenza-related office visits and other respiratory events than alternative egg-based vaccines.