This Phase 2/3 trial will enroll a total of 7320 male and female subjects randomized in a double-blind manner to receive either UB-612 or placebo. Assignment will be stratified by age (18 to 59 years and ≥60 years) and by presence/absence of comorbidities.

All subjects will receive 2 doses of the study vaccine, separated by 28 days, as an intramuscular (IM) injection.

Phase 2 and Phase 3 will start simultaneously; Phase 2 will enroll all Strata #1 to #4; Phase 3 will enroll Stratum #1 until the Data and Safety Monitoring Board (DSMB) has reviewed Phase 2 data through Day 43 and endorsed enrolment of Strata #2 to #4. All subjects in Phase 2 and Phase 3 will be followed for safety and efficacy.

This Phase 2/3 study also contains a Safety and Immunogenicity Cohort (N=1300) consisting of 1000 SARS-CoV-2 seronegative subjects (320 subjects enrolled in Phase 2 and 680 subjects enrolled in Phase 3) and 300 SARS-CoV-2 seropositive subjects enrolled in Phase 3.