inclusion criteria: * age ≥18 years at screening. * documented, previous completion of a primary vaccination regimen with locally authorized sars-cov-2 vaccine(s) or completion of primary plus 1 boost vaccination, with last vaccination at least 3 months before screening. "locally authorized" sars-cov-2 vaccines are those that have received market approval or emergency use authorization in the country of enrollment. * absence of acute medical illness, significant physical exam findings, or laboratory abnormalities, as determined by the investigator. * informed consent, provided by the subject prior to performance of any trial-specific procedures; the subject has read, signed, and dated an informed consent form (icf), having been advised of the risks and benefits of the trial in a language understood by the subject. * body mass index (bmi) ≥18.5 and \<40. * for female subjects of childbearing potential (wocbp) and male subjects who are sexually active with a wocbp, agreement to use an effective method of birth control from at least 30 days prior to administration of the vaccine until 30 days after the vaccination. a woman is considered of childbearing potential unless post-menopausal (defined as ≥12 months without a menstrual period at screening) or surgically sterilized (bilateral oophorectomy, bilateral tubal ligation, hysterectomy). acceptable contraception methods are restricted to abstinence (only acceptable if refraining from heterosexual intercourse during the period of 30 days prior to administration of the vaccine until 30 days after the vaccination), double barrier contraceptives, vasectomy, intrauterine contraceptive devices, or licensed hormonal products. * for wocbp, a negative serum pregnancy test at screening. * negative tests for human immunodeficiency virus antibody (anti hiv), hepatitis b surface antigen (hbsag), and antibody to hepatitis c virus (hcv).

inclusion criteria: * age ≥18 years at screening. * documented, previous completion of a primary vaccination regimen with locally authorized sars-cov-2 vaccine(s) or completion of primary plus 1 boost vaccination, with last vaccination at least 3 months before screening. "locally authorized" sars-cov-2 vaccines are those that have received market approval or emergency use authorization in the country of enrollment. * absence of acute medical illness, significant physical exam findings, or laboratory abnormalities, as determined by the investigator. * informed consent, provided by the subject prior to performance of any trial-specific procedures; the subject has read, signed, and dated an informed consent form (icf), having been advised of the risks and benefits of the trial in a language understood by the subject. * body mass index (bmi) ≥18.5 and \<40. * for female subjects of childbearing potential (wocbp) and male subjects who are sexually active with a wocbp, agreement to use an effective method of birth control from at least 30 days prior to administration of the vaccine until 30 days after the vaccination. a woman is considered of childbearing potential unless post-menopausal (defined as ≥12 months without a menstrual period at screening) or surgically sterilized (bilateral oophorectomy, bilateral tubal ligation, hysterectomy). acceptable contraception methods are restricted to abstinence (only acceptable if refraining from heterosexual intercourse during the period of 30 days prior to administration of the vaccine until 30 days after the vaccination), double barrier contraceptives, vasectomy, intrauterine contraceptive devices, or licensed hormonal products. * for wocbp, a negative serum pregnancy test at screening. * negative tests for human immunodeficiency virus antibody (anti hiv), hepatitis b surface antigen (hbsag), and antibody to hepatitis c virus (hcv).

inclusion criteria: age ≥18 years at screening. documented, previous completion of a primary vaccination regimen with locally authorized sars-cov-2 vaccine(s) or completion of primary plus 1 boost vaccination, with last vaccination at least 3 months before screening. "locally authorized" sars-cov-2 vaccines are those that have received market approval or emergency use authorization in the country of enrollment. absence of acute medical illness, significant physical exam findings, or laboratory abnormalities, as determined by the investigator. informed consent, provided by the subject prior to performance of any trial-specific procedures; the subject has read, signed, and dated an informed consent form (icf), having been advised of the risks and benefits of the trial in a language understood by the subject. body mass index (bmi) ≥18.5 and <40. for female subjects of childbearing potential (wocbp) and male subjects who are sexually active with a wocbp, agreement to use an effective method of birth control from at least 30 days prior to administration of the vaccine until 30 days after the vaccination. a woman is considered of childbearing potential unless post-menopausal (defined as ≥12 months without a menstrual period at screening) or surgically sterilized (bilateral oophorectomy, bilateral tubal ligation, hysterectomy). acceptable contraception methods are restricted to abstinence (only acceptable if refraining from heterosexual intercourse during the period of 30 days prior to administration of the vaccine until 30 days after the vaccination), double barrier contraceptives, vasectomy, intrauterine contraceptive devices, or licensed hormonal products. for wocbp, a negative serum pregnancy test at screening. negative tests for human immunodeficiency virus antibody (anti hiv), hepatitis b surface antigen (hbsag), and antibody to hepatitis c virus (hcv).

inclusion criteria: age ≥18 years at screening. documented, previous completion of a primary vaccination regimen with locally authorized sars-cov-2 vaccine(s) or completion of primary plus 1 boost vaccination, with last vaccination at least 3 months before screening. "locally authorized" sars-cov-2 vaccines are those that have received market approval or emergency use authorization in the country of enrollment. absence of acute medical illness, significant physical exam findings, or laboratory abnormalities, as determined by the investigator. informed consent, provided by the subject prior to performance of any trial-specific procedures; the subject has read, signed, and dated an informed consent form (icf), having been advised of the risks and benefits of the trial in a language understood by the subject. body mass index (bmi) ≥18.5 and <40. for female subjects of childbearing potential (wocbp) and male subjects who are sexually active with a wocbp, agreement to use an effective method of birth control from at least 30 days prior to administration of the vaccine until 30 days after the vaccination. a woman is considered of childbearing potential unless post-menopausal (defined as ≥12 months without a menstrual period at screening) or surgically sterilized (bilateral oophorectomy, bilateral tubal ligation, hysterectomy). acceptable contraception methods are restricted to abstinence (only acceptable if refraining from heterosexual intercourse during the period of 30 days prior to administration of the vaccine until 30 days after the vaccination), double barrier contraceptives, vasectomy, intrauterine contraceptive devices, or licensed hormonal products. for wocbp, a negative serum pregnancy test at screening. negative tests for human immunodeficiency virus antibody (anti hiv), hepatitis b surface antigen (hbsag), and antibody to hepatitis c virus (hcv).

inclusion criteria: age ≥18 years at screening. documented, previous administration of locally authorized sars-cov-2 vaccine(s) for primary vaccination only or for primary plus 1 boost vaccination, with last vaccination at least 3 months before screening. "locally authorized" sars-cov-2 vaccines are those that have received market approval or emergency use authorization in the country of enrollment. absence of acute medical illness, significant physical exam findings, or laboratory abnormalities, as determined by the investigator. informed consent, provided by the subject prior to performance of any trial-specific procedures; the subject has read, signed, and dated an informed consent form (icf), having been advised of the risks and benefits of the trial in a language understood by the subject. body mass index (bmi) ≥18.5 and <40. for female subjects of childbearing potential (wocbp) and male subjects who are sexually active with a wocbp, agreement to use an effective method of birth control from at least 30 days prior to administration of the vaccine until 30 days after the vaccination. a woman is considered of childbearing potential unless post-menopausal (defined as ≥12 months without a menstrual period at screening) or surgically sterilized (bilateral oophorectomy, bilateral tubal ligation, hysterectomy). acceptable contraception methods are restricted to abstinence (only acceptable if refraining from heterosexual intercourse during the period of 30 days prior to administration of the vaccine until 30 days after the vaccination), double barrier contraceptives, vasectomy, intrauterine contraceptive devices, or licensed hormonal products. for wocbp, a negative serum pregnancy test at screening. negative tests for human immunodeficiency virus antibody (anti hiv), hepatitis b surface antigen (hbsag), and antibody to hepatitis c virus (hcv).

inclusion criteria: age ≥18 years at screening. documented, previous administration of locally authorized sars-cov-2 vaccine(s) for primary vaccination only or for primary plus 1 boost vaccination, with last vaccination at least 3 months before screening. "locally authorized" sars-cov-2 vaccines are those that have received market approval or emergency use authorization in the country of enrollment. absence of acute medical illness, significant physical exam findings, or laboratory abnormalities, as determined by the investigator. informed consent, provided by the subject prior to performance of any trial-specific procedures; the subject has read, signed, and dated an informed consent form (icf), having been advised of the risks and benefits of the trial in a language understood by the subject. body mass index (bmi) ≥18.5 and <40. for female subjects of childbearing potential (wocbp) and male subjects who are sexually active with a wocbp, agreement to use an effective method of birth control from at least 30 days prior to administration of the vaccine until 30 days after the vaccination. a woman is considered of childbearing potential unless post-menopausal (defined as ≥12 months without a menstrual period at screening) or surgically sterilized (bilateral oophorectomy, bilateral tubal ligation, hysterectomy). acceptable contraception methods are restricted to abstinence (only acceptable if refraining from heterosexual intercourse during the period of 30 days prior to administration of the vaccine until 30 days after the vaccination), double barrier contraceptives, vasectomy, intrauterine contraceptive devices, or licensed hormonal products. for wocbp, a negative serum pregnancy test at screening. negative tests for human immunodeficiency virus antibody (anti hiv), hepatitis b surface antigen (hbsag), and antibody to hepatitis c virus (hcv).

inclusion criteria: age ≥18 years at screening documented, previous vaccination with an authorized sars-cov-2 vaccination regimen with last vaccination at least 6 months (cohort 1) or at least 3 months (cohorts 2 and 3) before screening. "authorized" sars-cov-2 vaccines include the following: comirnaty (pfizer/biontech), spikevax (moderna), vaxzevria (astrazeneca), janssen covid-19 vaccine (johnson&johnson), and any other vaccine that has received market approval or emergency use authorization in the us or eu. absence of acute medical illness, significant physical exam findings, or laboratory abnormalities, as determined by the investigator. informed consent, provided by the subject prior to performance of any trial-specific procedures; the subject has read, signed, and dated an informed consent form (icf), having been advised of the risks and benefits of the trial in a language understood by the subject. body mass index (bmi) ≥18.5 and <40 for wocbp, a negative serum pregnancy test at screening. wocbp and male subjects who are sexually active with a wocbp, agreement to use an effective method of birth control from at least 30 days prior to administration of the vaccine until 30 days after the vaccination. negative tests for human immunodeficiency virus antibody (anti-hiv), hepatitis b surface antigen (hbsag), and antibody to hepatitis c virus (hcv).

inclusion criteria: age ≥18 years at screening documented, previous vaccination with an authorized sars-cov-2 vaccination regimen with last vaccination at least 6 months (cohort 1) or at least 3 months (cohorts 2 and 3) before screening. "authorized" sars-cov-2 vaccines include the following: comirnaty (pfizer/biontech), spikevax (moderna), vaxzevria (astrazeneca), janssen covid-19 vaccine (johnson&johnson), and any other vaccine that has received market approval or emergency use authorization in the us or eu. absence of acute medical illness, significant physical exam findings, or laboratory abnormalities, as determined by the investigator. informed consent, provided by the subject prior to performance of any trial-specific procedures; the subject has read, signed, and dated an informed consent form (icf), having been advised of the risks and benefits of the trial in a language understood by the subject. body mass index (bmi) ≥18.5 and <40 for wocbp, a negative serum pregnancy test at screening. wocbp and male subjects who are sexually active with a wocbp, agreement to use an effective method of birth control from at least 30 days prior to administration of the vaccine until 30 days after the vaccination. negative tests for human immunodeficiency virus antibody (anti-hiv), hepatitis b surface antigen (hbsag), and antibody to hepatitis c virus (hcv).