Flublok v. Standard Dose Vaccine Effectiveness Among Kaiser Permanente Northern California Adults 18-64 Years

The overall objective of this study is to describe the effectiveness of Flublok Quadrivalent vaccine compared to standard dose inactivated influenza vaccine (SD-IIV) in adults 18 through 64 years of age. During this study, Flublok Quadrivalent or SD-IIV will be administered according to the guidelines in the Prescribing Information materials and only to persons for whom it is indicated. The 2018-2019, 2019-2020, and 2020-2021 formulations of recombinant influenza vaccine (Flublok Quadrivalent vaccine) and SD-IIV will be evaluated for outcomes including all polymerase chain reaction (PCR)-confirmed influenza, PCR-confirmed hospitalized influenza, hospitalized community-acquired pneumonia and cardio-respiratory events.