After being informed about the study and potential risks, all participants giving written informed consent will be evaluated for eligibility criteria. At day 0, participants who meet the eligibility requirements will undergo a thorough medical evaluation and a urine pregnancy test (if applicable). Eligible participants will be placed in one of three vaccination interval groups (4, 8 or 12 weeks between the first two Covid -19 (recombinante) vaccine doses) in a randomized manner, via a computer program created by the statistical annalist. Both participant and research team will know the allocated group.~Eligible and consenting participants will have a blood sample collected (IgG Anti-S antibodies) and immediately after be administered a third dose of the Covid-19 (recombinante) vaccine. Participants will be instructed to fill out an adverse events journal for solicited adverse events for 7 days and non-solicited adverse events for 28 days after each dose. The research team will contact the participant remotely at least twice during the first two weeks.~The participant will return for a follow-up visit to the research center 28 days after each dose, to evaluate adverse events, collect blood samples (IgG Anti-S antibodies) and undergo a thorough medical evaluation.~The participant will also return to the research center to collect blood samples (IgG Anti-S antibodies) in two more follow-up visits: 6 and 12 months after vaccination with Covid-19 (recombinante).
The purpose of this clinical trial is to compare antibody response and safety of the Covid-19 (recombinante) vaccine according to different time intervals between the first two doses (4, 8 and 12 weeks) and serologic status immediately before the vaccine.