A Trial Evaluating the Safety and Immunogenicity of 3 COVID-19 SARS-CoV-2 RNA Vaccines in Healthy Adults

The study will initially enroll approximately 72 adult participants into 2 cohorts (A and B). Cohort A is further sub-divided into two sub-cohorts which include 12 participants who are seronegative, not previously vaccinated at screening (Sub-cohort A1) and 24 participants who are seropositive, not previously vaccinated at screening (Sub-cohort A2). Within the first cohort (Cohort A), Sub-cohort A1 will include a total of 12 adult participants ≥21 to ≤65 years of age who have not been previously vaccinated with a SARS-CoV-2 vaccine. Sub-cohort A2 will include a total of 24 adult participants ≥21 to ≤65 years of age who have not been previously vaccinated with a SARS-CoV-2 vaccine. Study vaccines will be given as 2 doses separated by 28 days. The second cohort (Cohort B) will include a total of 36 adult participants ≥21 to ≤65 years of age who have been previously vaccinated (5 months or longer prior to study enrollment) with SARS-CoV-2 vaccine. Study vaccines will be given as single doses. Additional cohorts may increase the age range of participants up to 80 years of age.