This clinical study will be consisted of 7 clinical visits and one long-term follow-up visit. Subjects will also be unblinded at Visit 5, subjects in placebo group will withdraw from the study and subjects in vaccine group will be encouraged to have 3rd dose of vaccination (Day 197~Day 242) at Visit 6. Those who received 3rd dose will have Visit 7 (14 days after Visit 6) to check the booster effect. After Day 197, subjects will enter the long-term follow-up with a safety call bi-monthly.
This is a phase II, observer-blind, multiple-centre, randomized, placebo-controlled study to evaluate the immunogenicity, safety, tolerability and lot consistency of 2 doses of UB-612 vaccine in adolescent, younger and elderly adults. Around 3850 adult subjects will be randomized to be composed of the core group, while around 385 adolescents will be randomized to be the supplementary group. Subjects will be unblinded at Visit 5, and subjects in the vaccine group will be encouraged to have 3rd dose of vaccination.