Relative Vaccine Effectiveness of Adjuvanted Quadrivalent Inactivated Influenza Vaccine (aIIV4) vs High-Dose Quadrivalent Inactivated Influenza Vaccine (HD-IIV4) for Prevention of Lab-confirmed Influenza Medical Encounters

In this study, each objective will be evaluated for each season individually and in a combined analysis. The primary objective is to assess the relative vaccine effectiveness of aIIV4 vs HD-IIV4 for prevention of polymerase-chain reaction (PCR) confirmed influenza. The secondary objectives are to: assess the relative vaccine effectiveness of aIIV4 vs HD-IIV4 for prevention of PCR-confirmed influenza in an emergency room or inpatient hospitalization setting; pneumonia in an emergency room or inpatient hospitalization setting; pneumonia or influenza in an emergency room or inpatient hospitalization setting; cardio-respiratory events in an emergency room or inpatient hospitalization setting; and cardiovascular events in an emergency room or inpatient hospitalization setting. Additional analyses may be conducted stratified by subgroups of comorbidities and age groups.

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