Relative Effectiveness of Influenza Vaccines Among the United States Elderly, 2018–2019

Background Studies among individuals ages ≥65 years have found a moderately higher relative vaccine effectiveness (RVE) for the high-dose (HD) influenza vaccine compared with standard-dose (SD) products for most seasons. Studies during the A(H3N2)-dominated 2017–2018 season showed slightly higher RVE for the cell-cultured vaccine compared with SD egg-based vaccines. We investigated the RVE of influenza vaccines among Medicare beneficiaries ages ≥65 years during the 2018–2019 season. Methods This is a retrospective cohort study using inverse probability of treatment weighting and Poisson regression to evaluate RVE in preventing influenza hospital encounters. Results Among 12 777 214 beneficiaries, the egg-based adjuvanted (RVE, 7.7%; 95% confidence interval [CI], 3.9%–11.4%) and HD (RVE, 4.9%; 95% CI, 1.7%–8.1%) vaccines were marginally more effective than the egg-based quadrivalent vaccines. The cell-cultured quadrivalent vaccine was not significantly more effective than the egg-based quadrivalent vaccine (RVE, 2.5%; 95% CI, −2.4% to 7.3%). Conclusions We did not find major effectiveness differences between licensed vaccines used among the elderly during the 2018–2019 season. Consistent with prior research, we found that the egg-based adjuvanted and HD vaccines were slightly more effective than the egg-based quadrivalent vaccines.