This is a Phase I double-blind, randomized, placebo-controlled study in 206 healthy adults, 18-49 years of age, inclusive, who are in good health and meet all eligibility criteria.

The purpose of this dose-escalation clinical study is to assess the safety, tolerability/reactogenicity, and immunogenicity of H3N2 M2SR investigational vaccines for the prevention of influenza when delivered at higher dosages or in two doses.

Eligible subjects will be screened and randomized to receive two administrations 28 days apart of Sing2016 M2SR at three dose levels (low, medium, high), Bris10 M2SR at one dose level (low), or placebo in a 1:1:1:1:1 ratio. Study duration will be approximately 8 months with subject participation duration of approximately 7 months. The primary study objective is to assess the safety and reactogenicity of a monovalent live single replication influenza H3N2 M2SR vaccine.