This is a randomized, double-blind, placebo-controlled Phase 1b study to evaluate the safety and immunogenicity of the investigational Sing2016 M2SR H3N2 influenza vaccine delivered intranasally to a healthy adult population age 50 to 85 years.

120 Eligible subjects will be randomized 2:1 to receive one administration of Sing2016 M2SR or placebo followed by a dose of age-appropriate licensed inactivated influenza vaccine (IIV) at least 28 days later. Two lead-in groups of adults ages 50-64 years (Cohort 1) and 65 - 85 years (Cohort 2) will be followed by enrollment of an expansion group, ages 65 - 85 (Cohort 3). Safety data will be reviewed between enrollment of successive cohorts.