inclusion criteria: 1. male or female participants between the ages of 18 and 55 years, (a-cohorts), and 65 and 85 years (b-cohorts), inclusive at study entry. 2. body mass index (bmi) over 19 kg/m\^2 and under 32 kg/m\^2 and weight at least 50 kg at study entry. 3. healthy participants who are determined by medical history, physical examination, and clinical judgment of the investigator to be eligible for inclusion in the study. note: healthy participants may have stable pre-existing disease defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrollment. 4. able to give personal signed informed consent and willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, and other study procedures. 5. participants must agree not to be vaccinated with any sars-cov-2 vaccine, starting after visit 0 and continuously until 6 months after receiving the first study immunization. 6. participants who have previously received at least two vaccinations with a licensed sars-cov-2 mrna vaccine (spikevax/moderna and/or comirnaty/pfizer administered as two-dose primary series with or without booster vaccination\[s\]) with the last vaccination having occurred at least 3 months prior. 7. participants who are sars-cov-2 vaccine-naïve (applies to vaccine-naïve group of cohort a only): 1. currently not working in occupations with high risk of exposure to sars-cov-2 (e.g., healthcare worker, emergency response personnel) (vaccine-naïve group of cohort a only). 2. no previous vaccination with any sars-cov-2 vaccine (vaccine-naïve group of cohort a only). 8. if the participant is a woman of child bearing potential (wocbp) must: 1. have a negative beta-human chorionic gonadotropin (hcg)-urine test at visit 0 and visit 1. 2. agree to practice a highly effective form of contraception for at least 14 days prior to study vaccination and continuously until a minimum of 28 days after receiving the last immunization. 3. agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the study, starting after visit 0 and continuously until 28 days after receiving the last immunization. note: women that are postmenopausal or permanently sterilized will be considered as not having reproductive potential. 9. men who are sexually active with a wocbp and have not had a vasectomy must agree to practice a highly effective form of contraception with their female partner during the study, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization. 10. men must be willing to refrain from sperm donation, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization.

inclusion criteria: 1. male or female participants between the ages of 18 and 55 years, (a-cohorts), and 65 and 85 years (b-cohorts), inclusive at study entry. 2. body mass index (bmi) over 19 kg/m\^2 and under 32 kg/m\^2 and weight at least 50 kg at study entry. 3. healthy participants who are determined by medical history, physical examination, and clinical judgment of the investigator to be eligible for inclusion in the study. note: healthy participants may have stable pre-existing disease defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrollment. 4. able to give personal signed informed consent and willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, and other study procedures. 5. participants must agree not to be vaccinated with any sars-cov-2 vaccine, starting after visit 0 and continuously until 6 months after receiving the first study immunization. 6. participants who have previously received at least two vaccinations with a licensed sars-cov-2 mrna vaccine (spikevax/moderna and/or comirnaty/pfizer administered as two-dose primary series with or without booster vaccination\[s\]) with the last vaccination having occurred at least 3 months prior. 7. participants who are sars-cov-2 vaccine-naïve (applies to vaccine-naïve group of cohort a only): 1. currently not working in occupations with high risk of exposure to sars-cov-2 (e.g., healthcare worker, emergency response personnel) (vaccine-naïve group of cohort a only). 2. no previous vaccination with any sars-cov-2 vaccine (vaccine-naïve group of cohort a only). 8. if the participant is a woman of child bearing potential (wocbp) must: 1. have a negative beta-human chorionic gonadotropin (hcg)-urine test at visit 0 and visit 1. 2. agree to practice a highly effective form of contraception for at least 14 days prior to study vaccination and continuously until a minimum of 28 days after receiving the last immunization. 3. agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the study, starting after visit 0 and continuously until 28 days after receiving the last immunization. note: women that are postmenopausal or permanently sterilized will be considered as not having reproductive potential. 9. men who are sexually active with a wocbp and have not had a vasectomy must agree to practice a highly effective form of contraception with their female partner during the study, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization. 10. men must be willing to refrain from sperm donation, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization.

inclusion criteria: male or female participants between the ages of 18 and 55 years, (a-cohorts), and 65 and 85 years (b-cohorts), inclusive at study entry. body mass index (bmi) over 19 kg/m^2 and under 32 kg/m^2 and weight at least 50 kg at study entry. healthy participants who are determined by medical history, physical examination, and clinical judgment of the investigator to be eligible for inclusion in the study. note: healthy participants may have stable pre-existing disease defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrollment. able to give personal signed informed consent and willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, and other study procedures. participants must agree not to be vaccinated with any sars-cov-2 vaccine, starting after visit 0 and continuously until 6 months after receiving the first study immunization. participants who have previously received at least two vaccinations with a licensed sars-cov-2 mrna vaccine (spikevax/moderna and/or comirnaty/pfizer administered as two-dose primary series with or without booster vaccination[s]) with the last vaccination having occurred at least 3 months prior. participants who are sars-cov-2 vaccine-naïve (applies to vaccine-naïve group of cohort a only): currently not working in occupations with high risk of exposure to sars-cov-2 (e.g., healthcare worker, emergency response personnel) (vaccine-naïve group of cohort a only). no previous vaccination with any sars-cov-2 vaccine (vaccine-naïve group of cohort a only). if the participant is a woman of child bearing potential (wocbp) must: have a negative beta-human chorionic gonadotropin (hcg)-urine test at visit 0 and visit 1. agree to practice a highly effective form of contraception for at least 14 days prior to study vaccination and continuously until a minimum of 28 days after receiving the last immunization. agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the study, starting after visit 0 and continuously until 28 days after receiving the last immunization. note: women that are postmenopausal or permanently sterilized will be considered as not having reproductive potential. men who are sexually active with a wocbp and have not had a vasectomy must agree to practice a highly effective form of contraception with their female partner during the study, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization. men must be willing to refrain from sperm donation, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization.

inclusion criteria: male or female participants between the ages of 18 and 55 years, (a-cohorts), and 65 and 85 years (b-cohorts), inclusive at study entry. body mass index (bmi) over 19 kg/m^2 and under 32 kg/m^2 and weight at least 50 kg at study entry. healthy participants who are determined by medical history, physical examination, and clinical judgment of the investigator to be eligible for inclusion in the study. note: healthy participants may have stable pre-existing disease defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrollment. able to give personal signed informed consent and willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, and other study procedures. participants must agree not to be vaccinated with any sars-cov-2 vaccine, starting after visit 0 and continuously until 6 months after receiving the first study immunization. participants who have previously received at least two vaccinations with a licensed sars-cov-2 mrna vaccine (spikevax/moderna and/or comirnaty/pfizer administered as two-dose primary series with or without booster vaccination[s]) with the last vaccination having occurred at least 3 months prior. participants who are sars-cov-2 vaccine-naïve (applies to vaccine-naïve group of cohort a only): currently not working in occupations with high risk of exposure to sars-cov-2 (e.g., healthcare worker, emergency response personnel) (vaccine-naïve group of cohort a only). no previous vaccination with any sars-cov-2 vaccine (vaccine-naïve group of cohort a only). if the participant is a woman of child bearing potential (wocbp) must: have a negative beta-human chorionic gonadotropin (hcg)-urine test at visit 0 and visit 1. agree to practice a highly effective form of contraception for at least 14 days prior to study vaccination and continuously until a minimum of 28 days after receiving the last immunization. agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the study, starting after visit 0 and continuously until 28 days after receiving the last immunization. note: women that are postmenopausal or permanently sterilized will be considered as not having reproductive potential. men who are sexually active with a wocbp and have not had a vasectomy must agree to practice a highly effective form of contraception with their female partner during the study, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization. men must be willing to refrain from sperm donation, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization.

inclusion criteria: male or female participants between the ages of 18 and 55 years, (a-cohorts), and 65 and 85 years (b-cohorts), inclusive at study entry. body mass index (bmi) over 19 kg/m^2 and under 32 kg/m^2 and weight at least 50 kg at study entry. healthy participants who are determined by medical history, physical examination, and clinical judgment of the investigator to be eligible for inclusion in the study. note: healthy participants may have stable pre-existing disease defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrollment. able to give personal signed informed consent and willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, and other study procedures. participants must agree not to be vaccinated with any sars-cov-2 vaccine, starting after visit 0 and continuously until 6 months after receiving the first study immunization. participants who have previously received at least two vaccinations with a licensed sars-cov-2 mrna vaccine (spikevax/moderna and/or comirnaty/pfizer administered as two-dose primary series with or without booster vaccination[s]) with the last vaccination having occurred at least 3 months prior. participants who are sars-cov-2 vaccine-naïve (applies to vaccine-naïve group of cohort a only): currently not working in occupations with high risk of exposure to sars-cov-2 (e.g., healthcare worker, emergency response personnel) (vaccine-naïve group of cohort a only). no previous vaccination with any sars-cov-2 vaccine (vaccine-naïve group of cohort a only). if the participant is a woman of child bearing potential (wocbp) must: have a negative beta-human chorionic gonadotropin (hcg)-urine test at visit 0 and visit 1. agree to practice a highly effective form of contraception for at least 14 days prior to study vaccination and continuously until a minimum of 28 days after receiving the last immunization. agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the study, starting after visit 0 and continuously until 28 days after receiving the last immunization. note: women that are postmenopausal or permanently sterilized will be considered as not having reproductive potential. note: methods that can achieve a failure rate of less than 1% per year when used consistently and correctly are considered as highly effective contraceptive methods. men who are sexually active with a wocbp and have not had a vasectomy must agree to practice a highly effective form of contraception with their female partner during the study, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization. men must be willing to refrain from sperm donation, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization.

inclusion criteria: male or female participants between the ages of 18 and 55 years, (a-cohorts), and 65 and 85 years (b-cohorts), inclusive at study entry. body mass index (bmi) over 19 kg/m^2 and under 32 kg/m^2 and weight at least 50 kg at study entry. healthy participants who are determined by medical history, physical examination, and clinical judgment of the investigator to be eligible for inclusion in the study. note: healthy participants may have stable pre-existing disease defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrollment. able to give personal signed informed consent and willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, and other study procedures. participants must agree not to be vaccinated with any sars-cov-2 vaccine, starting after visit 0 and continuously until 6 months after receiving the first study immunization. participants who have previously received at least two vaccinations with a licensed sars-cov-2 mrna vaccine (spikevax/moderna and/or comirnaty/pfizer administered as two-dose primary series with or without booster vaccination[s]) with the last vaccination having occurred at least 3 months prior. participants who are sars-cov-2 vaccine-naïve (applies to vaccine-naïve group of cohort a only): currently not working in occupations with high risk of exposure to sars-cov-2 (e.g., healthcare worker, emergency response personnel) (vaccine-naïve group of cohort a only). no previous vaccination with any sars-cov-2 vaccine (vaccine-naïve group of cohort a only). if the participant is a woman of child bearing potential (wocbp) must: have a negative beta-human chorionic gonadotropin (hcg)-urine test at visit 0 and visit 1. agree to practice a highly effective form of contraception for at least 14 days prior to study vaccination and continuously until a minimum of 28 days after receiving the last immunization. agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the study, starting after visit 0 and continuously until 28 days after receiving the last immunization. note: women that are postmenopausal or permanently sterilized will be considered as not having reproductive potential. note: methods that can achieve a failure rate of less than 1% per year when used consistently and correctly are considered as highly effective contraceptive methods. men who are sexually active with a wocbp and have not had a vasectomy must agree to practice a highly effective form of contraception with their female partner during the study, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization. men must be willing to refrain from sperm donation, starting from visit 1 (pre-dose) and continuously until a minimum of 28 days after receiving the last immunization.

inclusion criteria: male or female participants between the ages of 18 and 55 years, (a-cohorts), and 65 and 85 years (b-cohorts), inclusive at study entry. body mass index (bmi) over 19 kg/m^2 and under 30 kg/m^2 and weight at least 50 kg at study entry. healthy participants who are determined by medical history, physical examination, and clinical judgment of the investigator to be eligible for inclusion in the study. note: healthy participants may have stable pre-existing disease defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrollment. able to give personal signed informed consent and willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, and other study procedures. participants must agree not to be vaccinated with any sars-cov-2 vaccine, starting after visit 0 and continuously until 6 months after receiving the first study immunization. participants who have previously received at least two vaccinations with sars-cov-2 mrna vaccine (full primary sequence with or without booster vaccination) with the last vaccination having occurred at least 3 months prior. participants who are sars-cov-2 vaccine-naïve (applies to vaccine-naïve group of cohort a only): currently not working in occupations with high risk of exposure to sars-cov-2 (e.g., healthcare worker, emergency response personnel) (vaccine-naïve group of cohort a only). no previous vaccination with any sars-cov-2 vaccine (vaccine-naïve group of cohort a only). if the participant is a woman of child bearing potential (wocbp) must: have a negative beta-human chorionic gonadotropin (hcg)-urine test at visit 0 and visit 1. agree to practice a highly effective form of contraception during the study, starting after visit 0 and continuously until 30 days after receiving the last immunization. agree to require their male partners to use condoms during sexual contact (unless male partners are sterilized or infertile). confirm that they practiced at least one highly effective form of contraception for the at least 14 days prior to visit 0. agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the study, starting after visit 0 and continuously until 30 days after receiving the last immunization. note: women that are postmenopausal or permanently sterilized will be considered as not having reproductive potential. note: methods that can achieve a failure rate of less than 1% per year when used consistently and correctly are considered as highly effective contraceptive methods. men who are sexually active with a wocbp and have not had a vasectomy must agree to practice a highly effective form of contraception with their female partner during the study, starting after visit 0 and continuously until 30 days after receiving the last immunization. men must be willing to refrain from sperm donation, starting after visit 0 and continuously until 30 days after receiving the last immunization.

inclusion criteria: male or female participants between the ages of 18 and 55 years, (a-cohorts), and 65 and 85 years (b-cohorts), inclusive at study entry. body mass index (bmi) over 19 kg/m^2 and under 30 kg/m^2 and weight at least 50 kg at study entry. healthy participants who are determined by medical history, physical examination, and clinical judgment of the investigator to be eligible for inclusion in the study. note: healthy participants may have stable pre-existing disease defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrollment. able to give personal signed informed consent and willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, and other study procedures. participants must agree not to be vaccinated with any sars-cov-2 vaccine, starting after visit 0 and continuously until 6 months after receiving the first study immunization. participants who have previously received at least two vaccinations with sars-cov-2 mrna vaccine (full primary sequence with or without booster vaccination) with the last vaccination having occurred at least 3 months prior. participants who are sars-cov-2 vaccine-naïve (applies to vaccine-naïve group of cohort a only): currently not working in occupations with high risk of exposure to sars-cov-2 (e.g., healthcare worker, emergency response personnel) (vaccine-naïve group of cohort a only). no previous vaccination with any sars-cov-2 vaccine (vaccine-naïve group of cohort a only). if the participant is a woman of child bearing potential (wocbp) must: have a negative beta-human chorionic gonadotropin (hcg)-urine test at visit 0 and visit 1. agree to practice a highly effective form of contraception during the study, starting after visit 0 and continuously until 30 days after receiving the last immunization. agree to require their male partners to use condoms during sexual contact (unless male partners are sterilized or infertile). confirm that they practiced at least one highly effective form of contraception for the at least 14 days prior to visit 0. agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the study, starting after visit 0 and continuously until 30 days after receiving the last immunization. note: women that are postmenopausal or permanently sterilized will be considered as not having reproductive potential. note: methods that can achieve a failure rate of less than 1% per year when used consistently and correctly are considered as highly effective contraceptive methods. men who are sexually active with a wocbp and have not had a vasectomy must agree to practice a highly effective form of contraception with their female partner during the study, starting after visit 0 and continuously until 30 days after receiving the last immunization. men must be willing to refrain from sperm donation, starting after visit 0 and continuously until 30 days after receiving the last immunization.