* current active infection with covid-19. * positive for sars-cov-2 by nasal swab polymerase chain reaction (pcr) at screening. * currently receiving treatment or prevention agents with activity against sars-cov-2. * breastfeeding, pregnant, or planning to become pregnant during the course of the study. * received or plans to receive any non-study provided sars-cov-2 vaccine (including boost) during the study period (except for part d). * received or plans to receive any live, attenuated vaccine within 28 days before or after study vaccination. * received or plans to receive any subunit or killed vaccine within 14 days before or after vaccination. * received or plans to receive immunoglobulins and/or any blood products within the 3 months preceding the planned administration of first study vaccination or at any time during the study. * currently active viral infection of hepatitis b virus or hepatitis c virus. additional exclusion criteria for plwh: * screening cd4+ t cell count ≤200 cells/mcl. * viral load ≥10,000 virus particles/ml. * history of opportunistic illness indicative of stage 3 hiv infection. * acute febrile illness within 4 weeks before the first vaccination. additional exclusion criterion for part d (grt-r918) cohorts d3, d4, d7, and d8: - received last dose of any authorized sars-cov-2 vaccine series within 2 months prior to study vaccine.

* current active infection with covid-19. * positive for sars-cov-2 by nasal swab polymerase chain reaction (pcr) at screening. * currently receiving treatment or prevention agents with activity against sars-cov-2. * breastfeeding, pregnant, or planning to become pregnant during the course of the study. * received or plans to receive any non-study provided sars-cov-2 vaccine (including boost) during the study period (except for part d). * received or plans to receive any live, attenuated vaccine within 28 days before or after study vaccination. * received or plans to receive any subunit or killed vaccine within 14 days before or after vaccination. * received or plans to receive immunoglobulins and/or any blood products within the 3 months preceding the planned administration of first study vaccination or at any time during the study. * currently active viral infection of hepatitis b virus or hepatitis c virus. additional exclusion criteria for plwh: * screening cd4+ t cell count ≤200 cells/mcl. * viral load ≥10,000 virus particles/ml. * history of opportunistic illness indicative of stage 3 hiv infection. * acute febrile illness within 4 weeks before the first vaccination. additional exclusion criterion for part d (grt-r918) cohorts d3, d4, d7, and d8: - received last dose of any authorized sars-cov-2 vaccine series within 2 months prior to study vaccine.

current active infection with covid-19. positive for sars-cov-2 by nasal swab polymerase chain reaction (pcr) at screening. currently receiving treatment or prevention agents with activity against sars-cov-2. breastfeeding, pregnant, or planning to become pregnant during the course of the study. received or plans to receive any non-study provided sars-cov-2 vaccine (including boost) during the study period (except for part d). received or plans to receive any live, attenuated vaccine within 28 days before or after study vaccination. received or plans to receive any subunit or killed vaccine within 14 days before or after vaccination. received or plans to receive immunoglobulins and/or any blood products within the 3 months preceding the planned administration of first study vaccination or at any time during the study. currently active viral infection of hepatitis b virus or hepatitis c virus. additional exclusion criteria for plwh: screening cd4+ t cell count ≤200 cells/mcl. viral load ≥10,000 virus particles/ml. history of opportunistic illness indicative of stage 3 hiv infection. acute febrile illness within 4 weeks before the first vaccination. additional exclusion criterion for part d (grt-r918) cohorts d3, d4, d7, and d8: - received last dose of any authorized sars-cov-2 vaccine series within 2 months prior to study vaccine.

current active infection with covid-19. positive for sars-cov-2 by nasal swab polymerase chain reaction (pcr) at screening. currently receiving treatment or prevention agents with activity against sars-cov-2. breastfeeding, pregnant, or planning to become pregnant during the course of the study. received or plans to receive any non-study provided sars-cov-2 vaccine (including boost) during the study period (except for part d). received or plans to receive any live, attenuated vaccine within 28 days before or after study vaccination. received or plans to receive any subunit or killed vaccine within 14 days before or after vaccination. received or plans to receive immunoglobulins and/or any blood products within the 3 months preceding the planned administration of first study vaccination or at any time during the study. currently active viral infection of hepatitis b virus or hepatitis c virus. additional exclusion criteria for plwh: screening cd4+ t cell count ≤200 cells/mcl. viral load ≥10,000 virus particles/ml. history of opportunistic illness indicative of stage 3 hiv infection. acute febrile illness within 4 weeks before the first vaccination. additional exclusion criterion for part d (grt-r918) cohorts d3, d4, d7, and d8: - received last dose of any authorized sars-cov-2 vaccine series within 2 months prior to study vaccine.