inclusion criteria: * male or non-pregnant female at least 18 years and no more than 65 years of age at enrollment (parts a, b, and c only). * no previous sars-cov-2 infection or recovered. * hiv-negative status confirmed by laboratory testing. additional inclusion criteria for plwh: * serum positive hiv test or history of hiv infection. * on anti-retroviral therapy for at least 3 months before screening and clinically stable. additional inclusion criteria for part d (grt-r918): * male or non-pregnant female between 18 and \<60 years of age at enrollment. * male or non-pregnant female greater than or equal to 60 years of age at enrollment. * received any authorized sars-cov-2 vaccine series at least 2 months prior to study vaccine.

inclusion criteria: * male or non-pregnant female at least 18 years and no more than 65 years of age at enrollment (parts a, b, and c only). * no previous sars-cov-2 infection or recovered. * hiv-negative status confirmed by laboratory testing. additional inclusion criteria for plwh: * serum positive hiv test or history of hiv infection. * on anti-retroviral therapy for at least 3 months before screening and clinically stable. additional inclusion criteria for part d (grt-r918): * male or non-pregnant female between 18 and \<60 years of age at enrollment. * male or non-pregnant female greater than or equal to 60 years of age at enrollment. * received any authorized sars-cov-2 vaccine series at least 2 months prior to study vaccine.

inclusion criteria: male or non-pregnant female at least 18 years and no more than 65 years of age at enrollment (parts a, b, and c only). no previous sars-cov-2 infection or recovered. hiv-negative status confirmed by laboratory testing. additional inclusion criteria for plwh: serum positive hiv test or history of hiv infection. on anti-retroviral therapy for at least 3 months before screening and clinically stable. additional inclusion criteria for part d (grt-r918): male or non-pregnant female between 18 and <60 years of age at enrollment. male or non-pregnant female greater than or equal to 60 years of age at enrollment. received any authorized sars-cov-2 vaccine series at least 2 months prior to study vaccine.

inclusion criteria: male or non-pregnant female at least 18 years and no more than 65 years of age at enrollment (parts a, b, and c only). no previous sars-cov-2 infection or recovered. hiv-negative status confirmed by laboratory testing. additional inclusion criteria for plwh: serum positive hiv test or history of hiv infection. on anti-retroviral therapy for at least 3 months before screening and clinically stable. additional inclusion criteria for part d (grt-r918): male or non-pregnant female between 18 and <60 years of age at enrollment. male or non-pregnant female greater than or equal to 60 years of age at enrollment. received any authorized sars-cov-2 vaccine series at least 2 months prior to study vaccine.