inclusion criteria: 1. understands and agrees to comply with the study procedures and provides written informed consent. 2. passes written comprehension test outlining study procedures. 3. male or female, aged 18 to 59 years or aged \>60 years at randomization. 4. canadian frailty scale score of 0 to 6 (see appendix 1). 5. women of childbearing potential (wocbp) and men must agree to practice medically effective contraception from 28 days before the first vaccination until 1 month after the last vaccination (i.e., a 3-month period). the acceptable effective contraception methods include the following: 1. barrier method (such as condoms, diaphragm, or cervical cap) used in conjunction with spermicide 2. intrauterine device 3. prescription hormonal contraceptive taken or administered via oral (pill), transdermal (patch), subdermal, or im route 4. sterilization of a female participant's monogamous male partner prior to entry into the study 5. abstinence 6. for wocbp, serum pregnancy test must be negative at screening; urine pregnancy test must be negative within 24 hours before vaccination. 7. lactating female participants must agree not to breastfeed or store breast milk for 3 days after each vaccination. a substituted formula is recommended during these periods. 8. negative serum antibodies (igg) against sars-cov-2 n protein at screening except for 300 subjects in the seropositive cohort (phase 3 only). 9. negative result for rt-pcr screening of saliva or nasal mid-turbinate sample for sars-cov-2 within 2 days before vaccination. 10. at high risk of sars-cov-2 exposure due to occupation (e.g., health care providers, first responders, service industry workers, etc.), residence (multi-generational home, long-term care facilities, etc.), or environment with high incidence (e.g., public transportation), including geographic area. 11. judged to be healthy or stable with pre-existing medical condition that did not require significant change in medication or hospitalization in 3 months before enrollment or who, in the judgement of the investigator are unlikely to require a significant change in therapy or hospitalization for worsening disease in the 3 months after enrollment. 12. must be able to read, understand, and complete questionnaires in the electronic clinical outcome assessment (ecoa) system. 13. plans to reside within study area for the duration of the study. 14. able to comply with study procedures, in the opinion of the investigator.

inclusion criteria: 1. understands and agrees to comply with the study procedures and provides written informed consent. 2. passes written comprehension test outlining study procedures. 3. male or female, aged 18 to 59 years or aged \>60 years at randomization. 4. canadian frailty scale score of 0 to 6 (see appendix 1). 5. women of childbearing potential (wocbp) and men must agree to practice medically effective contraception from 28 days before the first vaccination until 1 month after the last vaccination (i.e., a 3-month period). the acceptable effective contraception methods include the following: 1. barrier method (such as condoms, diaphragm, or cervical cap) used in conjunction with spermicide 2. intrauterine device 3. prescription hormonal contraceptive taken or administered via oral (pill), transdermal (patch), subdermal, or im route 4. sterilization of a female participant's monogamous male partner prior to entry into the study 5. abstinence 6. for wocbp, serum pregnancy test must be negative at screening; urine pregnancy test must be negative within 24 hours before vaccination. 7. lactating female participants must agree not to breastfeed or store breast milk for 3 days after each vaccination. a substituted formula is recommended during these periods. 8. negative serum antibodies (igg) against sars-cov-2 n protein at screening except for 300 subjects in the seropositive cohort (phase 3 only). 9. negative result for rt-pcr screening of saliva or nasal mid-turbinate sample for sars-cov-2 within 2 days before vaccination. 10. at high risk of sars-cov-2 exposure due to occupation (e.g., health care providers, first responders, service industry workers, etc.), residence (multi-generational home, long-term care facilities, etc.), or environment with high incidence (e.g., public transportation), including geographic area. 11. judged to be healthy or stable with pre-existing medical condition that did not require significant change in medication or hospitalization in 3 months before enrollment or who, in the judgement of the investigator are unlikely to require a significant change in therapy or hospitalization for worsening disease in the 3 months after enrollment. 12. must be able to read, understand, and complete questionnaires in the electronic clinical outcome assessment (ecoa) system. 13. plans to reside within study area for the duration of the study. 14. able to comply with study procedures, in the opinion of the investigator.

inclusion criteria: understands and agrees to comply with the study procedures and provides written informed consent. passes written comprehension test outlining study procedures. male or female, aged 18 to 59 years or aged >60 years at randomization. canadian frailty scale score of 0 to 6 (see appendix 1). women of childbearing potential (wocbp) and men must agree to practice medically effective contraception from 28 days before the first vaccination until 1 month after the last vaccination (i.e., a 3-month period). the acceptable effective contraception methods include the following: barrier method (such as condoms, diaphragm, or cervical cap) used in conjunction with spermicide intrauterine device prescription hormonal contraceptive taken or administered via oral (pill), transdermal (patch), subdermal, or im route sterilization of a female participant's monogamous male partner prior to entry into the study abstinence for wocbp, serum pregnancy test must be negative at screening; urine pregnancy test must be negative within 24 hours before vaccination. lactating female participants must agree not to breastfeed or store breast milk for 3 days after each vaccination. a substituted formula is recommended during these periods. negative serum antibodies (igg) against sars-cov-2 n protein at screening except for 300 subjects in the seropositive cohort (phase 3 only). negative result for rt-pcr screening of saliva or nasal mid-turbinate sample for sars-cov-2 within 2 days before vaccination. at high risk of sars-cov-2 exposure due to occupation (e.g., health care providers, first responders, service industry workers, etc.), residence (multi-generational home, long-term care facilities, etc.), or environment with high incidence (e.g., public transportation), including geographic area. judged to be healthy or stable with pre-existing medical condition that did not require significant change in medication or hospitalization in 3 months before enrollment or who, in the judgement of the investigator are unlikely to require a significant change in therapy or hospitalization for worsening disease in the 3 months after enrollment. must be able to read, understand, and complete questionnaires in the electronic clinical outcome assessment (ecoa) system. plans to reside within study area for the duration of the study. able to comply with study procedures, in the opinion of the investigator.

inclusion criteria: understands and agrees to comply with the study procedures and provides written informed consent. passes written comprehension test outlining study procedures. male or female, aged 18 to 59 years or aged >60 years at randomization. canadian frailty scale score of 0 to 6 (see appendix 1). women of childbearing potential (wocbp) and men must agree to practice medically effective contraception from 28 days before the first vaccination until 1 month after the last vaccination (i.e., a 3-month period). the acceptable effective contraception methods include the following: barrier method (such as condoms, diaphragm, or cervical cap) used in conjunction with spermicide intrauterine device prescription hormonal contraceptive taken or administered via oral (pill), transdermal (patch), subdermal, or im route sterilization of a female participant's monogamous male partner prior to entry into the study abstinence for wocbp, serum pregnancy test must be negative at screening; urine pregnancy test must be negative within 24 hours before vaccination. lactating female participants must agree not to breastfeed or store breast milk for 3 days after each vaccination. a substituted formula is recommended during these periods. negative serum antibodies (igg) against sars-cov-2 n protein at screening except for 300 subjects in the seropositive cohort (phase 3 only). negative result for rt-pcr screening of saliva or nasal mid-turbinate sample for sars-cov-2 within 2 days before vaccination. at high risk of sars-cov-2 exposure due to occupation (e.g., health care providers, first responders, service industry workers, etc.), residence (multi-generational home, long-term care facilities, etc.), or environment with high incidence (e.g., public transportation), including geographic area. judged to be healthy or stable with pre-existing medical condition that did not require significant change in medication or hospitalization in 3 months before enrollment or who, in the judgement of the investigator are unlikely to require a significant change in therapy or hospitalization for worsening disease in the 3 months after enrollment. must be able to read, understand, and complete questionnaires in the electronic clinical outcome assessment (ecoa) system. plans to reside within study area for the duration of the study. able to comply with study procedures, in the opinion of the investigator.

inclusion criteria: 1. understands and agrees to comply with the study procedures and provides written informed consent. 2. passes written comprehension test outlining study procedures. 3. male or female, aged 18 to 59 years or aged >60 years at randomization. 4. canadian frailty scale score of 0 to 6 (see appendix 1). 5. women of childbearing potential (wocbp) and men must agree to practice medically effective contraception from 28 days before the first vaccination until 1 month after the last vaccination (i.e., a 3-month period). the acceptable effective contraception methods include the following: 1. barrier method (such as condoms, diaphragm, or cervical cap) used in conjunction with spermicide 2. intrauterine device 3. prescription hormonal contraceptive taken or administered via oral (pill), transdermal (patch), subdermal, or im route 4. sterilization of a female participant's monogamous male partner prior to entry into the study 5. abstinence 6. for wocbp, serum pregnancy test must be negative at screening; urine pregnancy test must be negative within 24 hours before vaccination. 7. lactating female participants must agree not to breastfeed or store breast milk for 3 days after each vaccination. a substituted formula is recommended during these periods. 8. negative serum antibodies (igg) against sars-cov-2 n protein at screening except for 300 subjects in the seropositive cohort (phase 3 only). 9. negative result for rt-pcr screening of saliva or nasal mid-turbinate sample for sars-cov-2 within 2 days before vaccination. 10. at high risk of sars-cov-2 exposure due to occupation (e.g., health care providers, first responders, service industry workers, etc.), residence (multi-generational home, long-term care facilities, etc.), or environment with high incidence (e.g., public transportation), including geographic area. 11. judged to be healthy or stable with pre-existing medical condition that did not require significant change in medication or hospitalization in 3 months before enrollment or who, in the judgement of the investigator are unlikely to require a significant change in therapy or hospitalization for worsening disease in the 3 months after enrollment. 12. must be able to read, understand, and complete questionnaires in the electronic clinical outcome assessment (ecoa) system. 13. plans to reside within study area for the duration of the study. 14. able to comply with study procedures, in the opinion of the investigator.

inclusion criteria: 1. understands and agrees to comply with the study procedures and provides written informed consent. 2. passes written comprehension test outlining study procedures. 3. male or female, aged 18 to 59 years or aged >60 years at randomization. 4. canadian frailty scale score of 0 to 6 (see appendix 1). 5. women of childbearing potential (wocbp) and men must agree to practice medically effective contraception from 28 days before the first vaccination until 1 month after the last vaccination (i.e., a 3-month period). the acceptable effective contraception methods include the following: 1. barrier method (such as condoms, diaphragm, or cervical cap) used in conjunction with spermicide 2. intrauterine device 3. prescription hormonal contraceptive taken or administered via oral (pill), transdermal (patch), subdermal, or im route 4. sterilization of a female participant's monogamous male partner prior to entry into the study 5. abstinence 6. for wocbp, serum pregnancy test must be negative at screening; urine pregnancy test must be negative within 24 hours before vaccination. 7. lactating female participants must agree not to breastfeed or store breast milk for 3 days after each vaccination. a substituted formula is recommended during these periods. 8. negative serum antibodies (igg) against sars-cov-2 n protein at screening except for 300 subjects in the seropositive cohort (phase 3 only). 9. negative result for rt-pcr screening of saliva or nasal mid-turbinate sample for sars-cov-2 within 2 days before vaccination. 10. at high risk of sars-cov-2 exposure due to occupation (e.g., health care providers, first responders, service industry workers, etc.), residence (multi-generational home, long-term care facilities, etc.), or environment with high incidence (e.g., public transportation), including geographic area. 11. judged to be healthy or stable with pre-existing medical condition that did not require significant change in medication or hospitalization in 3 months before enrollment or who, in the judgement of the investigator are unlikely to require a significant change in therapy or hospitalization for worsening disease in the 3 months after enrollment. 12. must be able to read, understand, and complete questionnaires in the electronic clinical outcome assessment (ecoa) system. 13. plans to reside within study area for the duration of the study. 14. able to comply with study procedures, in the opinion of the investigator.