inclusion criteria: 1. healthy adult male or females, ≥18 years of age at screening: 1. for the adult group: 18 to 54 years, inclusive, and 2. for the elderly group: 55 to 75 years, inclusive. 2. individuals who are willing and able to give an informed consent, prior to screening. 3. individuals who are able to comply with study requirements. 4. female subjects are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: 1. women of childbearing potential must have a negative serum pregnancy test at screening and a negative urine pregnancy test prior to each vaccination. they must be using a highly effective licensed method of birth control for 30 days prior to the first dose of the study vaccine/placebo and must agree to continue such precautions during the study until 60 days after the second dose of the study vaccine/placebo. 2. women not of childbearing potential, defined as surgically sterile (documented hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or postmenopausal (no menses for 12 months and follicle-stimulating hormone \[fsh\] in the postmenopausal range). 3. male subjects must agree to employ acceptable contraception from the day of first dose of the study vaccine/placebo until 90 days after the second dose of the study vaccine/placebo and also refrain from donating sperm during this period. 5. general good health based on medical history, physical examination, cardiac health evaluation, and clinical laboratory evaluations. participants in the elderly population who have medically stable, well-controlled co-morbidities may be enrolled at the discretion of the investigator. all clinical laboratory values should be within normal reference ranges unless confirmed by investigator or delegate as not clinically significant. one repeat evaluation of electrocardiogram (ecg), and clinical laboratory tests will be permitted, at the discretion of the investigator. 6. individuals agree to avoid strenuous exercise from screening to day 50. for the sars-cov-2 seropositive treatment group only (treatment groups 16 to 18): 7. serological or elisa confirmation of sars-cov-2; 8. no history of severe sars-cov-2 symptoms; 9. no sars-cov-2 symptoms at the time of the screening .

inclusion criteria: 1. healthy adult male or females, ≥18 years of age at screening: 1. for the adult group: 18 to 54 years, inclusive, and 2. for the elderly group: 55 to 75 years, inclusive. 2. individuals who are willing and able to give an informed consent, prior to screening. 3. individuals who are able to comply with study requirements. 4. female subjects are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: 1. women of childbearing potential must have a negative serum pregnancy test at screening and a negative urine pregnancy test prior to each vaccination. they must be using a highly effective licensed method of birth control for 30 days prior to the first dose of the study vaccine/placebo and must agree to continue such precautions during the study until 60 days after the second dose of the study vaccine/placebo. 2. women not of childbearing potential, defined as surgically sterile (documented hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or postmenopausal (no menses for 12 months and follicle-stimulating hormone \[fsh\] in the postmenopausal range). 3. male subjects must agree to employ acceptable contraception from the day of first dose of the study vaccine/placebo until 90 days after the second dose of the study vaccine/placebo and also refrain from donating sperm during this period. 5. general good health based on medical history, physical examination, cardiac health evaluation, and clinical laboratory evaluations. participants in the elderly population who have medically stable, well-controlled co-morbidities may be enrolled at the discretion of the investigator. all clinical laboratory values should be within normal reference ranges unless confirmed by investigator or delegate as not clinically significant. one repeat evaluation of electrocardiogram (ecg), and clinical laboratory tests will be permitted, at the discretion of the investigator. 6. individuals agree to avoid strenuous exercise from screening to day 50. for the sars-cov-2 seropositive treatment group only (treatment groups 16 to 18): 7. serological or elisa confirmation of sars-cov-2; 8. no history of severe sars-cov-2 symptoms; 9. no sars-cov-2 symptoms at the time of the screening .

inclusion criteria: healthy adult male or females, ≥18 years of age at screening: for the adult group: 18 to 54 years, inclusive, and for the elderly group: 55 to 75 years, inclusive. individuals who are willing and able to give an informed consent, prior to screening. individuals who are able to comply with study requirements. female subjects are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: women of childbearing potential must have a negative serum pregnancy test at screening and a negative urine pregnancy test prior to each vaccination. they must be using a highly effective licensed method of birth control for 30 days prior to the first dose of the study vaccine/placebo and must agree to continue such precautions during the study until 60 days after the second dose of the study vaccine/placebo. women not of childbearing potential, defined as surgically sterile (documented hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or postmenopausal (no menses for 12 months and follicle-stimulating hormone [fsh] in the postmenopausal range). male subjects must agree to employ acceptable contraception from the day of first dose of the study vaccine/placebo until 90 days after the second dose of the study vaccine/placebo and also refrain from donating sperm during this period. general good health based on medical history, physical examination, cardiac health evaluation, and clinical laboratory evaluations. participants in the elderly population who have medically stable, well-controlled co-morbidities may be enrolled at the discretion of the investigator. all clinical laboratory values should be within normal reference ranges unless confirmed by investigator or delegate as not clinically significant. one repeat evaluation of electrocardiogram (ecg), and clinical laboratory tests will be permitted, at the discretion of the investigator. individuals agree to avoid strenuous exercise from screening to day 50. for the sars-cov-2 seropositive treatment group only (treatment groups 16 to 18): serological or elisa confirmation of sars-cov-2; no history of severe sars-cov-2 symptoms; no sars-cov-2 symptoms at the time of the screening .

inclusion criteria: healthy adult male or females, ≥18 years of age at screening: for the adult group: 18 to 54 years, inclusive, and for the elderly group: 55 to 75 years, inclusive. individuals who are willing and able to give an informed consent, prior to screening. individuals who are able to comply with study requirements. female subjects are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: women of childbearing potential must have a negative serum pregnancy test at screening and a negative urine pregnancy test prior to each vaccination. they must be using a highly effective licensed method of birth control for 30 days prior to the first dose of the study vaccine/placebo and must agree to continue such precautions during the study until 60 days after the second dose of the study vaccine/placebo. women not of childbearing potential, defined as surgically sterile (documented hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or postmenopausal (no menses for 12 months and follicle-stimulating hormone [fsh] in the postmenopausal range). male subjects must agree to employ acceptable contraception from the day of first dose of the study vaccine/placebo until 90 days after the second dose of the study vaccine/placebo and also refrain from donating sperm during this period. general good health based on medical history, physical examination, cardiac health evaluation, and clinical laboratory evaluations. participants in the elderly population who have medically stable, well-controlled co-morbidities may be enrolled at the discretion of the investigator. all clinical laboratory values should be within normal reference ranges unless confirmed by investigator or delegate as not clinically significant. one repeat evaluation of electrocardiogram (ecg), and clinical laboratory tests will be permitted, at the discretion of the investigator. individuals agree to avoid strenuous exercise from screening to day 50. for the sars-cov-2 seropositive treatment group only (treatment groups 16 to 18): serological or elisa confirmation of sars-cov-2; no history of severe sars-cov-2 symptoms; no sars-cov-2 symptoms at the time of the screening .

inclusion criteria: healthy adult male or females, ≥18 years of age at screening: for the adult group: 18 to 54 years, inclusive, and for the elderly group: 55 to 75 years, inclusive. individuals who are willing and able to give an informed consent, prior to screening. individuals who are able to comply with study requirements. female subjects are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: women of childbearing potential must have a negative serum pregnancy test at screening and a negative urine pregnancy test prior to each vaccination. they must be using a highly effective licensed method of birth control for 30 days prior to the first dose of the study vaccine/placebo and must agree to continue such precautions during the study until 60 days after the second dose of the study vaccine/placebo. women not of childbearing potential, defined as surgically sterile (documented hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or postmenopausal (no menses for 12 months and follicle-stimulating hormone [fsh] in the postmenopausal range). male subjects must agree to employ acceptable contraception from the day of first dose of the study vaccine/placebo until 90 days after the second dose of the study vaccine/placebo and also refrain from donating sperm during this period. general good health based on medical history, physical examination, cardiac health evaluation, and clinical laboratory evaluations. participants in the elderly population who have medically stable, well-controlled co-morbidities may be enrolled at the discretion of the investigator. all clinical laboratory values should be within normal reference ranges unless confirmed by investigator or delegate as not clinically significant. one repeat evaluation of electrocardiogram (ecg), and clinical laboratory tests will be permitted, at the discretion of the investigator.

inclusion criteria: healthy adult male or females, ≥18 years of age at screening: for the adult group: 18 to 54 years, inclusive, and for the elderly group: 55 to 75 years, inclusive. individuals who are willing and able to give an informed consent, prior to screening. individuals who are able to comply with study requirements. female subjects are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: women of childbearing potential must have a negative serum pregnancy test at screening and a negative urine pregnancy test prior to each vaccination. they must be using a highly effective licensed method of birth control for 30 days prior to the first dose of the study vaccine/placebo and must agree to continue such precautions during the study until 60 days after the second dose of the study vaccine/placebo. women not of childbearing potential, defined as surgically sterile (documented hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or postmenopausal (no menses for 12 months and follicle-stimulating hormone [fsh] in the postmenopausal range). male subjects must agree to employ acceptable contraception from the day of first dose of the study vaccine/placebo until 90 days after the second dose of the study vaccine/placebo and also refrain from donating sperm during this period. general good health based on medical history, physical examination, cardiac health evaluation, and clinical laboratory evaluations. participants in the elderly population who have medically stable, well-controlled co-morbidities may be enrolled at the discretion of the investigator. all clinical laboratory values should be within normal reference ranges unless confirmed by investigator or delegate as not clinically significant. one repeat evaluation of electrocardiogram (ecg), and clinical laboratory tests will be permitted, at the discretion of the investigator.

inclusion criteria: 1. healthy adult male or females, ≥18 years of age at screening: 1. for the adult group: 18 to 54 years, inclusive, and 2. for the elderly group: 55 to 75 years, inclusive. 2. individuals who are willing and able to give an informed consent, prior to screening. 3. individuals who are able to comply with study requirements. 4. female subjects are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: 1. women of childbearing potential must have a negative serum pregnancy test at screening and a negative urine pregnancy test prior to each vaccination. they must be using a highly effective licensed method of birth control for 30 days prior to the first dose of the study vaccine/placebo and must agree to continue such precautions during the study until 60 days after the second dose of the study vaccine/placebo. 2. women not of childbearing potential, defined as surgically sterile (documented hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or postmenopausal (no menses for 12 months and follicle-stimulating hormone [fsh] in the postmenopausal range). 3. male subjects must agree to employ acceptable contraception from the day of first dose of the study vaccine/placebo until 90 days after the second dose of the study vaccine/placebo and also refrain from donating sperm during this period. 5. general good health based on medical history, physical examination, cardiac health evaluation, and clinical laboratory evaluations. participants in the elderly population who have medically stable, well-controlled co-morbidities may be enrolled at the discretion of the investigator. all clinical laboratory values should be within normal reference ranges unless confirmed by investigator or delegate as not clinically significant. one repeat evaluation of electrocardiogram (ecg), and clinical laboratory tests will be permitted, at the discretion of the investigator.

inclusion criteria: 1. healthy adult male or females, ≥18 years of age at screening: 1. for the adult group: 18 to 54 years, inclusive, and 2. for the elderly group: 55 to 75 years, inclusive. 2. individuals who are willing and able to give an informed consent, prior to screening. 3. individuals who are able to comply with study requirements. 4. female subjects are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply: 1. women of childbearing potential must have a negative serum pregnancy test at screening and a negative urine pregnancy test prior to each vaccination. they must be using a highly effective licensed method of birth control for 30 days prior to the first dose of the study vaccine/placebo and must agree to continue such precautions during the study until 60 days after the second dose of the study vaccine/placebo. 2. women not of childbearing potential, defined as surgically sterile (documented hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or postmenopausal (no menses for 12 months and follicle-stimulating hormone [fsh] in the postmenopausal range). 3. male subjects must agree to employ acceptable contraception from the day of first dose of the study vaccine/placebo until 90 days after the second dose of the study vaccine/placebo and also refrain from donating sperm during this period. 5. general good health based on medical history, physical examination, cardiac health evaluation, and clinical laboratory evaluations. participants in the elderly population who have medically stable, well-controlled co-morbidities may be enrolled at the discretion of the investigator. all clinical laboratory values should be within normal reference ranges unless confirmed by investigator or delegate as not clinically significant. one repeat evaluation of electrocardiogram (ecg), and clinical laboratory tests will be permitted, at the discretion of the investigator.