Participants were in the study for 6 months (approximately 180 days).
The main purpose of this Phase II study was to assess the safety and immunogenicity of a dose of Fluzone High-Dose (HD) Quadrivalent vaccine and a third dose or booster dose of Moderna coronavirus disease 19 (COVID-19) vaccine administered concomitantly or singly in adults 65 years of age and older having received their second dose of the 2-dose schedule of Moderna COVID-19 vaccine at least 5 months before enrollment in the study.