Influenza, Human

This is a Phase 3, randomized, parallel-group, comparator-controlled, observer-blind, multicenter study of immunogenicity and safety in approximately 7700 male and female adults aged 50 years and older (approximately equally split between two age groups: 50-64 years; 65 years and older), who are healthy or have stable comorbidities that increase their risk of complications from influenza infection. Three lots of aQIVc will be evaluated for consistency and pooled for the comparison with the 2 control vaccines. Subjects will be randomly assigned to receive 1 of 3 lots of aQIVc, QIV1, or QIV2 in a 1:1:1:2:2 ratio (for a 3:2:2 ratio for aQIVc, QIV1, and QIV2). The study will have a treatment period (Day 1 to Day 29) and a follow-up period (Day 30 up to Day 181); a subset of 770 subjects will be followed up up to Day 365.