COVID-19 mRNA vaccine (Fiocruz)

This is an exploratory phase 3, cohort randomized, observer-blind, multi-center study to evaluate the safety and immunogenicity of a 4th dose of various SARS-CoV-2 vaccines. There will be 04 study cohorts, that have previously received 03 doses of the indicated vaccine (s), divided into 10 groups; and each one of the 10 study groups will receive the 4th dose. This exploratory study will enroll up to 360 participants in 4 cohorts and a total of 10 groups: Cohort A (N=90), Cohort B (N= 90), Cohort C (N=150) and Cohort D (N=30). In cohorts A-C participants will be randomized 1:1:1 to three different 4th dose regimens. The number of proposed participants will provide a reasonable accurate descriptive summary of the safety and immunogenicity of the tested vaccination regimens.