Examining Vaccine Effectiveness of Flublok Relative to Standard Dose Inactivated Influenza Vaccine Among Kaiser Permanente Northern California Members Aged 18-64 Years

This study employs a cluster randomization design to examine the vaccine effectiveness of Flublok relative to that of other flu vaccines used at Kaiser Permanente Northern California over two influenza seasons (2018 to 2019 and 2019 to 2020), in Kaiser Permanente Northern California members aged 18 to 64 years (comparator vaccines will not include high-dose or live vaccines). The primary age group of interest is 50- to 64-year-olds. Primary outcomes may include: 1) an influenza diagnosis confirmed by polymerase chain reaction (PCR) test as positive for influenza (A or B), 2) hospitalization with a PCR-confirmed influenza diagnosis regardless of the principal discharge diagnosis, and 3) hospitalization for pneumonia in December through March (regardless of whether there is a PCR test). Secondary outcomes may include other flu-related events, such as cardiovascular events (e.g., myocardial infarction or stroke) and other respiratory outcomes.

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