inclusion criteria: 1. male or female ≥18 years of age. participation of individuals \>60 years will be limited to ≤ 10/ group. 2. individuals are willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures. 3. individuals are willing and able to give an informed consent, prior to screening. * individuals who received one of the following vaccination regimens 3 doses of pfizer/ wyeth; 3 doses of astrazeneca/fiocruz; or 2 doses of sinovac/butantan and 1 dose of astrazeneca, or eventually 3 doses of sinovac/butantan; or 2 doses of astrazeneca and 1 dose of alum/cpg-adjuvanted 9 µg or 30 µg clover scb-2019 vaccine (participants of study tp-scb-2019-002). * interval between last priming dose and 3rd dose minimum 3 months * interval between 3rd dose and 4th dose ≥ 4 months 4. healthy participants or participants with pre-existing medical conditions who are in a stable medical condition. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months before enrollment. 5. female participants are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: * women of non-childbearing potential; * women of childbearing potential (wocbp) must have a negative urine pregnancy test prior to study vaccination. a confirmatory serum pregnancy test may be conducted at the investigator's discretion. they must be using a highly effective licensed method of birth control for 30 days prior to the first vaccination and must agree to continue such precautions during the study until 90 days after the last study vaccination. 6. male participants must agree to employ acceptable contraception from the day of dose of the study vaccine until 6 months after the last dose of the study vaccine/comparator and also refrain from donating sperm during this period.

inclusion criteria: 1. male or female ≥18 years of age. participation of individuals \>60 years will be limited to ≤ 10/ group. 2. individuals are willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures. 3. individuals are willing and able to give an informed consent, prior to screening. * individuals who received one of the following vaccination regimens 3 doses of pfizer/ wyeth; 3 doses of astrazeneca/fiocruz; or 2 doses of sinovac/butantan and 1 dose of astrazeneca, or eventually 3 doses of sinovac/butantan; or 2 doses of astrazeneca and 1 dose of alum/cpg-adjuvanted 9 µg or 30 µg clover scb-2019 vaccine (participants of study tp-scb-2019-002). * interval between last priming dose and 3rd dose minimum 3 months * interval between 3rd dose and 4th dose ≥ 4 months 4. healthy participants or participants with pre-existing medical conditions who are in a stable medical condition. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months before enrollment. 5. female participants are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: * women of non-childbearing potential; * women of childbearing potential (wocbp) must have a negative urine pregnancy test prior to study vaccination. a confirmatory serum pregnancy test may be conducted at the investigator's discretion. they must be using a highly effective licensed method of birth control for 30 days prior to the first vaccination and must agree to continue such precautions during the study until 90 days after the last study vaccination. 6. male participants must agree to employ acceptable contraception from the day of dose of the study vaccine until 6 months after the last dose of the study vaccine/comparator and also refrain from donating sperm during this period.

inclusion criteria: male or female ≥18 years of age. participation of individuals >60 years will be limited to ≤ 10/ group. individuals are willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures. individuals are willing and able to give an informed consent, prior to screening. individuals who received one of the following vaccination regimens 3 doses of pfizer/ wyeth; 3 doses of astrazeneca/fiocruz; or 2 doses of sinovac/butantan and 1 dose of astrazeneca, or eventually 3 doses of sinovac/butantan; or 2 doses of astrazeneca and 1 dose of alum/cpg-adjuvanted 9 µg or 30 µg clover scb-2019 vaccine (participants of study tp-scb-2019-002). interval between last priming dose and 3rd dose minimum 3 months interval between 3rd dose and 4th dose ≥ 4 months healthy participants or participants with pre-existing medical conditions who are in a stable medical condition. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months before enrollment. female participants are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: women of non-childbearing potential; women of childbearing potential (wocbp) must have a negative urine pregnancy test prior to study vaccination. a confirmatory serum pregnancy test may be conducted at the investigator's discretion. they must be using a highly effective licensed method of birth control for 30 days prior to the first vaccination and must agree to continue such precautions during the study until 90 days after the last study vaccination. male participants must agree to employ acceptable contraception from the day of dose of the study vaccine until 6 months after the last dose of the study vaccine/comparator and also refrain from donating sperm during this period.

inclusion criteria: male or female ≥18 years of age. participation of individuals >60 years will be limited to ≤ 10/ group. individuals are willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures. individuals are willing and able to give an informed consent, prior to screening. individuals who received one of the following vaccination regimens 3 doses of pfizer/ wyeth; 3 doses of astrazeneca/fiocruz; or 2 doses of sinovac/butantan and 1 dose of astrazeneca, or eventually 3 doses of sinovac/butantan; or 2 doses of astrazeneca and 1 dose of alum/cpg-adjuvanted 9 µg or 30 µg clover scb-2019 vaccine (participants of study tp-scb-2019-002). interval between last priming dose and 3rd dose minimum 3 months interval between 3rd dose and 4th dose ≥ 4 months healthy participants or participants with pre-existing medical conditions who are in a stable medical condition. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months before enrollment. female participants are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: women of non-childbearing potential; women of childbearing potential (wocbp) must have a negative urine pregnancy test prior to study vaccination. a confirmatory serum pregnancy test may be conducted at the investigator's discretion. they must be using a highly effective licensed method of birth control for 30 days prior to the first vaccination and must agree to continue such precautions during the study until 90 days after the last study vaccination. male participants must agree to employ acceptable contraception from the day of dose of the study vaccine until 6 months after the last dose of the study vaccine/comparator and also refrain from donating sperm during this period.