Estimated Relative Effectiveness and Public Health Impact of Cell-Based Versus Egg-Based Influenza Vaccines During the 2022-2023 Season in the United States.

BACKGROUND: Egg adaptation can reduce the effectiveness of egg-based influenza vaccines. Previous studies have demonstrated improved effectiveness of cell versus egg-based quadrivalent influenza vaccines (QIVc and QIVe, respectively) during the 2017-2020 influenza seasons among persons aged ≥ 4 years. Here we evaluate the relative vaccine effectiveness (rVE) of QIVc versus QIVe in preventing test-confirmed influenza among persons aged 6 months to 64 years during the US 2022-2023 influenza season, along with the potential impact on influenza burden averted. METHODS: A retrospective test-negative design was applied to linked electronic health records and claims data from QIVc or QIVe recipients who were tested for influenza in routine outpatient care within 7 days of an acute respiratory or febrile illness. rVE was estimated by comparing the odds of testing positive among QIVc versus QIVe recipients, adjusted using doubly robust methodology. The influenza burden additionally averted by vaccination with QIVc versus QIVe was estimated using a published model. RESULTS: Of 43,086 patients included, 18.6% received QIVc and 81.4% received QIVe. The rVE of QIVc versus QIVe was 7.7% (95% CI, 0.9%-13.9%). Use of QIVc instead of QIVe during the 2022-23 influenza season would have prevented an additional 636,209 symptomatic cases of influenza, 314,130 outpatient visits, and 3759 hospitalizations. CONCLUSIONS: QIVc was superior to QIVe in the prevention of test-confirmed influenza among persons aged 6 months to 64 years during the US 2022-2023 influenza season. The rVE of 7.7% would translate to a substantially reduced influenza burden if QIVc were used over QIVe.