inclusion criteria: * employee of fundação oswaldo cruz, stationed in manguinhos campus, in rio de janeiro. * previous two-dose vaccine schedule with covid-19 (recombinante) in both doses, with an interval of8 or 12 weeks between doses. * a 6-month interval (5 to 7 month window) between the second and the third dose of covid-19 (recombinante) vaccine. * availability to participate during the entire study, and ability to follow study protocol strictly. * consent to supply personal contact information, such as telephone numbers, address and other information so the research team may contact the participant (for example, in case the participant fails to attend a scheduled visit without previous notice) * ability to understand and sign the volunteered and informed consent form, and ability to fill in the adverse events journal at home, according to the evaluation of the principal investigator ou delegated research team members. * understanding the impossibility of participating in another clinical trial while participating in this clinical trial.

inclusion criteria: * employee of fundação oswaldo cruz, stationed in manguinhos campus, in rio de janeiro. * previous two-dose vaccine schedule with covid-19 (recombinante) in both doses, with an interval of8 or 12 weeks between doses. * a 6-month interval (5 to 7 month window) between the second and the third dose of covid-19 (recombinante) vaccine. * availability to participate during the entire study, and ability to follow study protocol strictly. * consent to supply personal contact information, such as telephone numbers, address and other information so the research team may contact the participant (for example, in case the participant fails to attend a scheduled visit without previous notice) * ability to understand and sign the volunteered and informed consent form, and ability to fill in the adverse events journal at home, according to the evaluation of the principal investigator ou delegated research team members. * understanding the impossibility of participating in another clinical trial while participating in this clinical trial.

inclusion criteria: employee of fundação oswaldo cruz, stationed in manguinhos campus, in rio de janeiro. previous two-dose vaccine schedule with covid-19 (recombinante) in both doses, with an interval of8 or 12 weeks between doses. a 6-month interval (5 to 7 month window) between the second and the third dose of covid-19 (recombinante) vaccine. availability to participate during the entire study, and ability to follow study protocol strictly. consent to supply personal contact information, such as telephone numbers, address and other information so the research team may contact the participant (for example, in case the participant fails to attend a scheduled visit without previous notice) ability to understand and sign the volunteered and informed consent form, and ability to fill in the adverse events journal at home, according to the evaluation of the principal investigator ou delegated research team members. understanding the impossibility of participating in another clinical trial while participating in this clinical trial.

inclusion criteria: employee of fundação oswaldo cruz, stationed in manguinhos campus, in rio de janeiro. previous two-dose vaccine schedule with covid-19 (recombinante) in both doses, with an interval of8 or 12 weeks between doses. a 6-month interval (5 to 7 month window) between the second and the third dose of covid-19 (recombinante) vaccine. availability to participate during the entire study, and ability to follow study protocol strictly. consent to supply personal contact information, such as telephone numbers, address and other information so the research team may contact the participant (for example, in case the participant fails to attend a scheduled visit without previous notice) ability to understand and sign the volunteered and informed consent form, and ability to fill in the adverse events journal at home, according to the evaluation of the principal investigator ou delegated research team members. understanding the impossibility of participating in another clinical trial while participating in this clinical trial.