A Study to Assess the Safety and Immunogenicity of a COVID-19 Vaccine Booster in Healthy Adults

Eligible participants will undergo baseline assessments and will receive 1 injection of Prime-2-CoV\_Beta at Day 1. Participants will be followed up through 6 months post-booster vaccination. Follow-up visits will be performed at Days 4, 8, 15, 29, and Months 3 and 6, to assess the safety, tolerability, and immunogenicity of Prime-2-CoV\_Beta. Additional safety and tolerability data will be assessed 1 day and 2 days after booster vaccination (Days 2 and 3) by telephone. Initially, a total of 60 participants were planned to be vaccinated in 5 cohorts of 12 participants each. Dose ranging of Prime-2-CoV\_Beta was planned to be done by dose escalation with doses ranging from 3x104 plaque forming units (PFUs) up to 3x10\^7 PFUs. With protocol Version 7.0, Cohort 6 with 12 participants was added with 6x10\^7 PFU. With protocol Version 8.0, 1 additional cohort, Cohort 7 (1.2x10\^8 PFU, stratified by previous COVID-19 vaccinations and previous SARS-CoV-2 infections) with 24 participants will be added (total number thus 96 participants). Procedures for Cohorts 6 and 7 will be the same as for Cohorts 1 - 5, except that for some participants in Cohort 7 ORFV shedding in urine, saliva, blood, and stool will be evaluated.