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

• Number of adults 50-64 years old hospitalized with PCR-confirmed influenza[ Time Frame: Up to 8 months ]
  Patients who receive either Flublok or SD-IIV will be retroactively assessed for whether they had an inpatient stay and had a PCR-confirmed positive influenza test (≥14 days after vaccination) as recorded in their electronic medical record by the end of the influenza season (April 30).
• Number of adults 50-64 years old hospitalized with community-acquired pneumonia[ Time Frame: Up to 8 months ]
  Patients who receive either Flublok or SD-IIV will be retroactively assessed for whether they had an inpatient stay for community-acquired pneumonia (≥14 days after vaccination) as recorded in their electronic medical record by the end of the influenza season (April 30).
• Number of adults 50-64 years old hospitalized with cardio-respiratory events[ Time Frame: Up to 8 months ]
  Patients who receive either Flublok or SD-IIV will be retroactively assessed for whether they had an inpatient stay for cardio-respiratory events (e.g., pneumonia, other lower respiratory infections, acute myocardial infarction, congestive heart failure, stroke) (≥14 days after vaccination) as recorded in their electronic medical record by the end of the influenza season (April 30).

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 and 2019-2020 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.

• Biological: Flublok Quadrivalent
  Flublok Quadrivalent vaccine is a recombinant hemagglutinin influenza vaccine indicated for active immunization against disease caused by influenza A subtype viruses and type B viruses contained in the vaccine for adults 18 years of age and older. Use of recombinant DNA techniques to produce vaccine antigen expressed in cell culture is a method that avoids growing the influenza viruses in embryonated hen's eggs.
• Biological: Standard Dose Inactivated Influenza Vaccine (SD-IIV)
  For the 2018-2019 flu season, the primary SD-IIVs used will be Fluarix Quadrivalent and Flulaval Quadrivalent. The SD-IIV for the 2019-2020 flu season will be determined prior to the start of the season.

• : Flublok Recipients
  Kaiser Permanente Northern California members aged 18-64 years who receive Flublok Quadrivalent vaccine.
• : SD-IIV Recipients
  Kaiser Permanente Northern California members aged 18-64 years who receive standard dose inactivated influenza vaccine (SD-IIV).