inclusion criteria: * generally healthy male and female adults aged 18 years or older at the time of signing the informed consent form. * good general health as determined by screening evaluation no greater than 30 days before injection of study vaccine. note: participants who are overtly healthy as determined by medical evaluation or are considered medically stable according to the judgment of the investigator. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months prior to enrolment, and/or hospitalization within the entire study period is not anticipated. also, the participant appears likely to be able to remain in follow-up through the end of protocol-specified period. mild to moderate well-controlled comorbidities are allowed. * have received minimum of 2 doses of an authorized covid-19 vaccine at least 4 months prior to day 0. * male participant and females of child-bearing potential and heterosexually active, practice of adequate contraception for 30 days prior to injection, negative pregnancy test on the day of injection, and agreement to continue adequate contraception until 180 days after the injection. * written informed consent, after review of the consent form and having adequate opportunity to discuss the study with an investigator or a qualified designee.

inclusion criteria: * generally healthy male and female adults aged 18 years or older at the time of signing the informed consent form. * good general health as determined by screening evaluation no greater than 30 days before injection of study vaccine. note: participants who are overtly healthy as determined by medical evaluation or are considered medically stable according to the judgment of the investigator. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months prior to enrolment, and/or hospitalization within the entire study period is not anticipated. also, the participant appears likely to be able to remain in follow-up through the end of protocol-specified period. mild to moderate well-controlled comorbidities are allowed. * have received minimum of 2 doses of an authorized covid-19 vaccine at least 4 months prior to day 0. * male participant and females of child-bearing potential and heterosexually active, practice of adequate contraception for 30 days prior to injection, negative pregnancy test on the day of injection, and agreement to continue adequate contraception until 180 days after the injection. * written informed consent, after review of the consent form and having adequate opportunity to discuss the study with an investigator or a qualified designee.

inclusion criteria: generally healthy male and female adults aged 18 years or older at the time of signing the informed consent form. good general health as determined by screening evaluation no greater than 30 days before injection of study vaccine. note: participants who are overtly healthy as determined by medical evaluation or are considered medically stable according to the judgment of the investigator. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months prior to enrolment, and/or hospitalization within the entire study period is not anticipated. also, the participant appears likely to be able to remain in follow-up through the end of protocol-specified period. mild to moderate well-controlled comorbidities are allowed. have received minimum of 2 doses of an authorized covid-19 vaccine at least 4 months prior to day 0. male participant and females of child-bearing potential and heterosexually active, practice of adequate contraception for 30 days prior to injection, negative pregnancy test on the day of injection, and agreement to continue adequate contraception until 180 days after the injection. written informed consent, after review of the consent form and having adequate opportunity to discuss the study with an investigator or a qualified designee.

inclusion criteria: generally healthy male and female adults aged 18 years or older at the time of signing the informed consent form. good general health as determined by screening evaluation no greater than 30 days before injection of study vaccine. note: participants who are overtly healthy as determined by medical evaluation or are considered medically stable according to the judgment of the investigator. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months prior to enrolment, and/or hospitalization within the entire study period is not anticipated. also, the participant appears likely to be able to remain in follow-up through the end of protocol-specified period. mild to moderate well-controlled comorbidities are allowed. have received minimum of 2 doses of an authorized covid-19 vaccine at least 4 months prior to day 0. male participant and females of child-bearing potential and heterosexually active, practice of adequate contraception for 30 days prior to injection, negative pregnancy test on the day of injection, and agreement to continue adequate contraception until 180 days after the injection. written informed consent, after review of the consent form and having adequate opportunity to discuss the study with an investigator or a qualified designee.

inclusion criteria: generally healthy male and female adults aged 18 years or older at the time of signing the informed consent form. good general health as determined by screening evaluation no greater than 30 days before injection of study vaccine. note: participants who are overtly healthy as determined by medical evaluation or are considered medically stable according to the judgment of the investigator. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months prior to enrolment, and/or hospitalization within the entire study period is not anticipated. also, the participant appears likely to be able to remain in follow-up through the end of protocol-specified period. mild to moderate well-controlled comorbidities are allowed. have received minimum of 2 doses of an authorized covid-19 vaccine at least 6 months prior to day 0(not applicable for subjects in exploratory phase 2 study arm). if female of child-bearing potential and heterosexually active, practice of adequate contraception for 30 days prior to injection, negative pregnancy test on the day of injection, and agreement to continue adequate contraception until 180 days after the injection. written informed consent, after review of the consent form and having adequate opportunity to discuss the study with an investigator or a qualified designee. exploratory phase 2 study arm: unvaccinated participants with a documented history of infection with sars-cov-2 (positive pcr or serology for sars-cov-2) or positive sars-cov-2 antibody test at screening.

inclusion criteria: generally healthy male and female adults aged 18 years or older at the time of signing the informed consent form. good general health as determined by screening evaluation no greater than 30 days before injection of study vaccine. note: participants who are overtly healthy as determined by medical evaluation or are considered medically stable according to the judgment of the investigator. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months prior to enrolment, and/or hospitalization within the entire study period is not anticipated. also, the participant appears likely to be able to remain in follow-up through the end of protocol-specified period. mild to moderate well-controlled comorbidities are allowed. have received minimum of 2 doses of an authorized covid-19 vaccine at least 6 months prior to day 0(not applicable for subjects in exploratory phase 2 study arm). if female of child-bearing potential and heterosexually active, practice of adequate contraception for 30 days prior to injection, negative pregnancy test on the day of injection, and agreement to continue adequate contraception until 180 days after the injection. written informed consent, after review of the consent form and having adequate opportunity to discuss the study with an investigator or a qualified designee. exploratory phase 2 study arm: unvaccinated participants with a documented history of infection with sars-cov-2 (positive pcr or serology for sars-cov-2) or positive sars-cov-2 antibody test at screening.

inclusion criteria: generally healthy male and female adults aged 18 years or older at the time of signing the informed consent form. good general health as determined by screening evaluation no greater than 30 days before injection of study vaccine. note: participants who are overtly healthy as determined by medical evaluation or are considered medically stable according to the judgment of the investigator. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months prior to enrolment, and/or hospitalization within the entire study period is not anticipated. also, the participant appears likely to be able to remain in follow-up through the end of protocol-specified period. mild to moderate well-controlled comorbidities are allowed. have received 2 doses of an authorized covid-19 vaccine at least 6 months prior to recruitment(not applicable for subjects in exploratory phase 2 study arm). if female of child-bearing potential and heterosexually active, practice of adequate contraception for 30 days prior to injection, negative pregnancy test on the day of injection, and agreement to continue adequate contraception until 180 days after the injection. written informed consent, after review of the consent form and having adequate opportunity to discuss the study with an investigator or a qualified designee. exploratory phase 2 study arm: unvaccinated participants with a documented history of infection with sars-cov-2 (positive pcr or serology for sars-cov-2) or positive rapid sars-cov-2 antibody test at screening.

inclusion criteria: generally healthy male and female adults aged 18 years or older at the time of signing the informed consent form. good general health as determined by screening evaluation no greater than 30 days before injection of study vaccine. note: participants who are overtly healthy as determined by medical evaluation or are considered medically stable according to the judgment of the investigator. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months prior to enrolment, and/or hospitalization within the entire study period is not anticipated. also, the participant appears likely to be able to remain in follow-up through the end of protocol-specified period. mild to moderate well-controlled comorbidities are allowed. have received 2 doses of an authorized covid-19 vaccine at least 6 months prior to recruitment(not applicable for subjects in exploratory phase 2 study arm). if female of child-bearing potential and heterosexually active, practice of adequate contraception for 30 days prior to injection, negative pregnancy test on the day of injection, and agreement to continue adequate contraception until 180 days after the injection. written informed consent, after review of the consent form and having adequate opportunity to discuss the study with an investigator or a qualified designee. exploratory phase 2 study arm: unvaccinated participants with a documented history of infection with sars-cov-2 (positive pcr or serology for sars-cov-2) or positive rapid sars-cov-2 antibody test at screening.