inclusion criteria: * male and female participants at least 18 years of age; * individuals willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures; * individuals willing and able to give an informed consent, prior to screening; * healthy participants or participants with pre-existing medical conditions who are in a stable medical condition; * individuals who received primary vaccination series with one of the selected covid-19 vaccines (comirnaty, vaxzevria, or coronavac) ≥3 months prior to enrollment; or received primary series and a booster dose (≥3 months after primary series) of coronavac, ≥3 months prior to enrollment.

inclusion criteria: * male and female participants at least 18 years of age; * individuals willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures; * individuals willing and able to give an informed consent, prior to screening; * healthy participants or participants with pre-existing medical conditions who are in a stable medical condition; * individuals who received primary vaccination series with one of the selected covid-19 vaccines (comirnaty, vaxzevria, or coronavac) ≥3 months prior to enrollment; or received primary series and a booster dose (≥3 months after primary series) of coronavac, ≥3 months prior to enrollment.

inclusion criteria: male and female participants at least 18 years of age; individuals willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures; individuals willing and able to give an informed consent, prior to screening; healthy participants or participants with pre-existing medical conditions who are in a stable medical condition; individuals who received primary vaccination series with one of the selected covid-19 vaccines (comirnaty, vaxzevria, or coronavac) ≥3 months prior to enrollment; or received primary series and a booster dose (≥3 months after primary series) of coronavac, ≥3 months prior to enrollment.

inclusion criteria: male and female participants at least 18 years of age; individuals willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures; individuals willing and able to give an informed consent, prior to screening; healthy participants or participants with pre-existing medical conditions who are in a stable medical condition; individuals who received primary vaccination series with one of the selected covid-19 vaccines (comirnaty, vaxzevria, or coronavac) ≥3 months prior to enrollment; or received primary series and a booster dose (≥3 months after primary series) of coronavac, ≥3 months prior to enrollment.

inclusion criteria: male and female participants at least 18 years of age; individuals willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures; individuals willing and able to give an informed consent, prior to screening; healthy participants or participants with pre-existing medical conditions who are in a stable medical condition; individuals who received primary series with scb-2019 vaccine or one of the selected authorized or investigational covid-19 vaccines (comirnaty, covid-19 vaccine janssen, or coronavac) at least 3 months prior to enrollment.

inclusion criteria: male and female participants at least 18 years of age; individuals willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures; individuals willing and able to give an informed consent, prior to screening; healthy participants or participants with pre-existing medical conditions who are in a stable medical condition; individuals who received primary series with scb-2019 vaccine or one of the selected authorized or investigational covid-19 vaccines (comirnaty, covid-19 vaccine janssen, or coronavac) at least 3 months prior to enrollment.

inclusion criteria: male and female participants ≥18 years of age; individuals willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures; individuals willing and able to give an informed consent, prior to screening; healthy participants or participants with pre-existing medical conditions who are in a stable medical condition; individuals who received primary series with scb-2019 vaccine or one of the selected authorized or investigational covid-19 vaccines (comirnaty, covid-19 vaccine janssen, or coronavac) ≥6 months prior to enrollment. female participants of childbearing potential may be enrolled in the study, if the participant has practiced highly effective contraception for 30 days prior to vaccination, and has a negative pregnancy test on the day of vaccination and has agreed to continue highly effective contraception for 3 months after the last vaccination.

inclusion criteria: male and female participants ≥18 years of age; individuals willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures; individuals willing and able to give an informed consent, prior to screening; healthy participants or participants with pre-existing medical conditions who are in a stable medical condition; individuals who received primary series with scb-2019 vaccine or one of the selected authorized or investigational covid-19 vaccines (comirnaty, covid-19 vaccine janssen, or coronavac) ≥6 months prior to enrollment. female participants of childbearing potential may be enrolled in the study, if the participant has practiced highly effective contraception for 30 days prior to vaccination, and has a negative pregnancy test on the day of vaccination and has agreed to continue highly effective contraception for 3 months after the last vaccination.