The phase 2 is dose-ranging study which will recruit 360 subjects to compare two vaccine formulas to placebo (1:1:1), to evaluate the safety and immunogenicity of the vaccine. The subjects will be given 2 doses of investigational product with 28 days interval between doses.~One selected vaccine formula will be evaluated for safety and persistence antibody until 6 months after the last dose.
This trial is observer-blind, comparative, randomized, placebo-controlled phase 2 study. The population is healthy subjects aged 18 and above