inclusion criteria: adults 18 to 64 years of age, inclusive, at screening. willing and able to give informed consent prior to study enrollment and to comply with study procedures. female participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile [ie, hysterectomy, bilateral tubal ligation, or bilateral oophorectomy] or postmenopausal [defined as amenorrhea at least 12 consecutive months]) must agree to be heterosexually inactive from at least 28 days prior to enrollment and through the end of the study or agree to consistently use a medically acceptable method of contraception listed below from at least 28 days prior to enrollment and through the end of the study. condoms (male or female) with spermicide (if acceptable in country) diaphragm with spermicide cervical cap with spermicide intrauterine device oral or patch contraceptives norplant®, depo-provera®, or other in-country regulatory approved contraceptive method that is designed to protect against pregnancy abstinence, as a form of contraception, is acceptable if in line with the participant's lifestyle is medically stable, as determined by the investigator (based on a review of health status, vital signs [to include body temperature], medical history, and targeted physical examination [to include body weight]). vital signs must be within medically acceptable ranges prior to the first vaccination. agrees to not participate in any other sars-cov-2 prevention or treatment trials for the duration of the study. for previously vaccinated participants (groups c, d and h): documented receipt of 2 doses of the investigational novavax vaccine with matrix-m1 adjuvant (nvx-cov2373) administered approximately 21 days apart or 2 doses of a tga-authorized/approved covid-19 vaccine administered at least 60 days prior to first study vaccination.

inclusion criteria: adults 18 to 64 years of age, inclusive, at screening. willing and able to give informed consent prior to study enrollment and to comply with study procedures. female participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile [ie, hysterectomy, bilateral tubal ligation, or bilateral oophorectomy] or postmenopausal [defined as amenorrhea at least 12 consecutive months]) must agree to be heterosexually inactive from at least 28 days prior to enrollment and through the end of the study or agree to consistently use a medically acceptable method of contraception listed below from at least 28 days prior to enrollment and through the end of the study. condoms (male or female) with spermicide (if acceptable in country) diaphragm with spermicide cervical cap with spermicide intrauterine device oral or patch contraceptives norplant®, depo-provera®, or other in-country regulatory approved contraceptive method that is designed to protect against pregnancy abstinence, as a form of contraception, is acceptable if in line with the participant's lifestyle is medically stable, as determined by the investigator (based on a review of health status, vital signs [to include body temperature], medical history, and targeted physical examination [to include body weight]). vital signs must be within medically acceptable ranges prior to the first vaccination. agrees to not participate in any other sars-cov-2 prevention or treatment trials for the duration of the study. for previously vaccinated participants (groups c, d and h): documented receipt of 2 doses of the investigational novavax vaccine with matrix-m1 adjuvant (nvx-cov2373) administered approximately 21 days apart or 2 doses of a tga-authorized/approved covid-19 vaccine administered at least 60 days prior to first study vaccination.

inclusion criteria: 1. adults 18 to 64 years of age, inclusive, at screening. 2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. 3. female participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile [ie, hysterectomy, bilateral tubal ligation, or bilateral oophorectomy] or postmenopausal [defined as amenorrhea at least 12 consecutive months]) must agree to be heterosexually inactive from at least 28 days prior to enrollment and through the end of the study or agree to consistently use a medically acceptable method of contraception listed below from at least 28 days prior to enrollment and through the end of the study. 1. condoms (male or female) with spermicide (if acceptable in country) 2. diaphragm with spermicide 3. cervical cap with spermicide 4. intrauterine device 5. oral or patch contraceptives 6. norplant®, depo-provera®, or other in-country regulatory approved contraceptive method that is designed to protect against pregnancy 7. abstinence, as a form of contraception, is acceptable if in line with the participant's lifestyle 4. is medically stable, as determined by the investigator (based on a review of health status, vital signs [to include body temperature], medical history, and targeted physical examination [to include body weight]). vital signs must be within medically acceptable ranges prior to the first vaccination. 5. agrees to not participate in any other sars-cov-2 prevention or treatment trials for the duration of the study. for previously vaccinated participants (groups c, d and h): 6. documented receipt of 2 doses of the investigational novavax vaccine with matrix-m1 adjuvant (nvx-cov2373) administered approximately 21 days apart or 2 doses of a tga-authorized/approved covid-19 vaccine administered at least 60 days prior to first study vaccination.

inclusion criteria: 1. adults 18 to 64 years of age, inclusive, at screening. 2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. 3. female participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile [ie, hysterectomy, bilateral tubal ligation, or bilateral oophorectomy] or postmenopausal [defined as amenorrhea at least 12 consecutive months]) must agree to be heterosexually inactive from at least 28 days prior to enrollment and through the end of the study or agree to consistently use a medically acceptable method of contraception listed below from at least 28 days prior to enrollment and through the end of the study. 1. condoms (male or female) with spermicide (if acceptable in country) 2. diaphragm with spermicide 3. cervical cap with spermicide 4. intrauterine device 5. oral or patch contraceptives 6. norplant®, depo-provera®, or other in-country regulatory approved contraceptive method that is designed to protect against pregnancy 7. abstinence, as a form of contraception, is acceptable if in line with the participant's lifestyle 4. is medically stable, as determined by the investigator (based on a review of health status, vital signs [to include body temperature], medical history, and targeted physical examination [to include body weight]). vital signs must be within medically acceptable ranges prior to the first vaccination. 5. agrees to not participate in any other sars-cov-2 prevention or treatment trials for the duration of the study. for previously vaccinated participants (groups c, d and h): 6. documented receipt of 2 doses of the investigational novavax vaccine with matrix-m1 adjuvant (nvx-cov2373) administered approximately 21 days apart or 2 doses of a tga-authorized/approved covid-19 vaccine administered at least 60 days prior to first study vaccination.