inclusion criteria: * male and female healthy volunteers. * is age 18 and 65 years inclusive on study day 1. * judged by the investigator to be healthy based on medical history, physical examination, vital signs, and no significant electrocardiogram (ecg) abnormalities performed at screening. * able to provide informed consent form. * able and willing to comply with all study procedures over follow-up period of approximately 6 months. * have completed either a 2-dose primary vaccination series with pfizer biontech-bnt162b2 sars-cov-2 vaccine (p) or moderna mrna-1273 (m) (as authorized/approved or as investigational product in a clinical trial), or have completed the primary series and one homologous booster of pfizer biontech-bnt162b2 or mrna-1273 i.e, p-p-p and m-m-m; the last dose in all cases should have been administered at least 6 months prior to enrollment. * body mass index of 18-32 kg/m2, inclusive, at screening. * for female subjects with childbearing potential: must agree to avoid pregnancy from 21 days prior to study day 1 until at least 90 days after last study vaccination. women physically capable of pregnancy (not sterilized and still menstruating or within 1 year of the last menses if menopausal) in sexual relationships with men must use an acceptable method of avoiding pregnancy during this period. acceptable methods of avoiding pregnancy include a sterile sexual partner, hormonal contraceptives (oral, injection, transdermal patch, or implant), vaginal ring, intrauterine device (iud), or the combination of a condom or diaphragm. * men must be willing to refrain from sperm donation, starting after screening until 90 days after receiving the last vaccination. * male and female subjects must use a barrier method of contraception, from 21 days prior to study day 1 until at least 90 days after last study vaccination. barrier methods of contraception include: * male condoms * female condoms * female diaphragm ('cap')

inclusion criteria: * male and female healthy volunteers. * is age 18 and 65 years inclusive on study day 1. * judged by the investigator to be healthy based on medical history, physical examination, vital signs, and no significant electrocardiogram (ecg) abnormalities performed at screening. * able to provide informed consent form. * able and willing to comply with all study procedures over follow-up period of approximately 6 months. * have completed either a 2-dose primary vaccination series with pfizer biontech-bnt162b2 sars-cov-2 vaccine (p) or moderna mrna-1273 (m) (as authorized/approved or as investigational product in a clinical trial), or have completed the primary series and one homologous booster of pfizer biontech-bnt162b2 or mrna-1273 i.e, p-p-p and m-m-m; the last dose in all cases should have been administered at least 6 months prior to enrollment. * body mass index of 18-32 kg/m2, inclusive, at screening. * for female subjects with childbearing potential: must agree to avoid pregnancy from 21 days prior to study day 1 until at least 90 days after last study vaccination. women physically capable of pregnancy (not sterilized and still menstruating or within 1 year of the last menses if menopausal) in sexual relationships with men must use an acceptable method of avoiding pregnancy during this period. acceptable methods of avoiding pregnancy include a sterile sexual partner, hormonal contraceptives (oral, injection, transdermal patch, or implant), vaginal ring, intrauterine device (iud), or the combination of a condom or diaphragm. * men must be willing to refrain from sperm donation, starting after screening until 90 days after receiving the last vaccination. * male and female subjects must use a barrier method of contraception, from 21 days prior to study day 1 until at least 90 days after last study vaccination. barrier methods of contraception include: * male condoms * female condoms * female diaphragm ('cap')

inclusion criteria: male and female healthy volunteers. is age 18 and 65 years inclusive on study day 1. judged by the investigator to be healthy based on medical history, physical examination, vital signs, and no significant electrocardiogram (ecg) abnormalities performed at screening. able to provide informed consent form. able and willing to comply with all study procedures over follow-up period of approximately 6 months. have completed either a 2-dose primary vaccination series with pfizer biontech-bnt162b2 sars-cov-2 vaccine (p) or moderna mrna-1273 (m) (as authorized/approved or as investigational product in a clinical trial), or have completed the primary series and one homologous booster of pfizer biontech-bnt162b2 or mrna-1273 i.e, p-p-p and m-m-m; the last dose in all cases should have been administered at least 6 months prior to enrollment. body mass index of 18-32 kg/m2, inclusive, at screening. for female subjects with childbearing potential: must agree to avoid pregnancy from 21 days prior to study day 1 until at least 90 days after last study vaccination. women physically capable of pregnancy (not sterilized and still menstruating or within 1 year of the last menses if menopausal) in sexual relationships with men must use an acceptable method of avoiding pregnancy during this period. acceptable methods of avoiding pregnancy include a sterile sexual partner, hormonal contraceptives (oral, injection, transdermal patch, or implant), vaginal ring, intrauterine device (iud), or the combination of a condom or diaphragm. men must be willing to refrain from sperm donation, starting after screening until 90 days after receiving the last vaccination. male and female subjects must use a barrier method of contraception, from 21 days prior to study day 1 until at least 90 days after last study vaccination. barrier methods of contraception include: male condoms female condoms female diaphragm ('cap')

inclusion criteria: male and female healthy volunteers. is age 18 and 65 years inclusive on study day 1. judged by the investigator to be healthy based on medical history, physical examination, vital signs, and no significant electrocardiogram (ecg) abnormalities performed at screening. able to provide informed consent form. able and willing to comply with all study procedures over follow-up period of approximately 6 months. have completed either a 2-dose primary vaccination series with pfizer biontech-bnt162b2 sars-cov-2 vaccine (p) or moderna mrna-1273 (m) (as authorized/approved or as investigational product in a clinical trial), or have completed the primary series and one homologous booster of pfizer biontech-bnt162b2 or mrna-1273 i.e, p-p-p and m-m-m; the last dose in all cases should have been administered at least 6 months prior to enrollment. body mass index of 18-32 kg/m2, inclusive, at screening. for female subjects with childbearing potential: must agree to avoid pregnancy from 21 days prior to study day 1 until at least 90 days after last study vaccination. women physically capable of pregnancy (not sterilized and still menstruating or within 1 year of the last menses if menopausal) in sexual relationships with men must use an acceptable method of avoiding pregnancy during this period. acceptable methods of avoiding pregnancy include a sterile sexual partner, hormonal contraceptives (oral, injection, transdermal patch, or implant), vaginal ring, intrauterine device (iud), or the combination of a condom or diaphragm. men must be willing to refrain from sperm donation, starting after screening until 90 days after receiving the last vaccination. male and female subjects must use a barrier method of contraception, from 21 days prior to study day 1 until at least 90 days after last study vaccination. barrier methods of contraception include: male condoms female condoms female diaphragm ('cap')