inclusion criteria: adult participants : each participant in the adult main study and/or the booster amendment must meet all of the following criteria to be enrolled in this study: 1. adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars cov-2. 2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. 3. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile \[i.e., hysterectomy, bilateral tubal ligation, or bilateral oophorectomy\] 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. 6. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination at the booster visit. pediatric participants : each participant in the pediatric expansion and/or the booster amendment must meet all of the following criteria to be enrolled in this study: 1. pediatric participants 12 to \< 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. 2. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 3. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile \[ie, hysterectomy, bilateral tubal ligation, or bilateral oophorectomy\] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. agree to not participate in another sars-cov-2 prevention trial during the study follow-up. 5. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination. site-specific sub study: each participant in the substudy must meet all of the following criteria to be enrolled in this study: 1. be an active, enrolled participant in the 2019ncov-301 study. 2. adults 18 years of age or older or adolescents 12 to \< 18 years of age at initial screening for the parent study. 3. willing and able to give informed consent prior to substudy enrollment and to comply with extra study procedures. 4. documented receipt of the 2 doses of the primary series of nvx-cov2373 and the booster (third dose) of nvx-cov2373 in the parent protocol. the booster dose must have been administered at least 6 months prior to entering the substudy. 5. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile or postmenopausal) must agree to be heterosexually inactive from at least 28 days prior to entering and through the end of the substudy or agree to consistently use a medically acceptable method of contraception for the 28 days of follow-up for the substudy. 6. is medically stable, as determined by the investigator (based on review of health status, vital signs (to include body temperature) and targeted physical examination (if medically indicated by reported symptoms). vital signs must be within medically acceptable ranges prior to administration of study vaccination. 7. agree to not participate in any other non-nvx-cov2373 study during the substudy. note: for participants who develop covid-19, anti-sars-cov-2 therapy (approved, authorized or investigational) is permitted.

inclusion criteria: adult participants : each participant in the adult main study and/or the booster amendment must meet all of the following criteria to be enrolled in this study: 1. adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars cov-2. 2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. 3. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile \[i.e., hysterectomy, bilateral tubal ligation, or bilateral oophorectomy\] 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. 6. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination at the booster visit. pediatric participants : each participant in the pediatric expansion and/or the booster amendment must meet all of the following criteria to be enrolled in this study: 1. pediatric participants 12 to \< 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. 2. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 3. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile \[ie, hysterectomy, bilateral tubal ligation, or bilateral oophorectomy\] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. agree to not participate in another sars-cov-2 prevention trial during the study follow-up. 5. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination. site-specific sub study: each participant in the substudy must meet all of the following criteria to be enrolled in this study: 1. be an active, enrolled participant in the 2019ncov-301 study. 2. adults 18 years of age or older or adolescents 12 to \< 18 years of age at initial screening for the parent study. 3. willing and able to give informed consent prior to substudy enrollment and to comply with extra study procedures. 4. documented receipt of the 2 doses of the primary series of nvx-cov2373 and the booster (third dose) of nvx-cov2373 in the parent protocol. the booster dose must have been administered at least 6 months prior to entering the substudy. 5. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile or postmenopausal) must agree to be heterosexually inactive from at least 28 days prior to entering and through the end of the substudy or agree to consistently use a medically acceptable method of contraception for the 28 days of follow-up for the substudy. 6. is medically stable, as determined by the investigator (based on review of health status, vital signs (to include body temperature) and targeted physical examination (if medically indicated by reported symptoms). vital signs must be within medically acceptable ranges prior to administration of study vaccination. 7. agree to not participate in any other non-nvx-cov2373 study during the substudy. note: for participants who develop covid-19, anti-sars-cov-2 therapy (approved, authorized or investigational) is permitted.

inclusion criteria: adult participants : each participant in the adult main study and/or the booster amendment must meet all of the following criteria to be enrolled in this study: adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars cov-2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile [i.e., 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination at the booster visit. pediatric participants : each participant in the pediatric expansion and/or the booster amendment must meet all of the following criteria to be enrolled in this study: pediatric participants 12 to < 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. agree to not participate in another sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination. site-specific sub study: each participant in the substudy must meet all of the following criteria to be enrolled in this study: be an active, enrolled participant in the 2019ncov-301 study. adults 18 years of age or older or adolescents 12 to < 18 years of age at initial screening for the parent study. willing and able to give informed consent prior to substudy enrollment and to comply with extra study procedures. documented receipt of the 2 doses of the primary series of nvx-cov2373 and the booster (third dose) of nvx-cov2373 in the parent protocol. the booster dose must have been administered at least 6 months prior to entering the substudy. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile or postmenopausal) must agree to be heterosexually inactive from at least 28 days prior to entering and through the end of the substudy or agree to consistently use a medically acceptable method of contraception for the 28 days of follow-up for the substudy. is medically stable, as determined by the investigator (based on review of health status, vital signs (to include body temperature) and targeted physical examination (if medically indicated by reported symptoms). vital signs must be within medically acceptable ranges prior to administration of study vaccination. agree to not participate in any other non-nvx-cov2373 study during the substudy. note: for participants who develop covid-19, anti-sars-cov-2 therapy (approved, authorized or investigational) is permitted.

inclusion criteria: adult participants : each participant in the adult main study and/or the booster amendment must meet all of the following criteria to be enrolled in this study: adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars cov-2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile [i.e., 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination at the booster visit. pediatric participants : each participant in the pediatric expansion and/or the booster amendment must meet all of the following criteria to be enrolled in this study: pediatric participants 12 to < 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. agree to not participate in another sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination. site-specific sub study: each participant in the substudy must meet all of the following criteria to be enrolled in this study: be an active, enrolled participant in the 2019ncov-301 study. adults 18 years of age or older or adolescents 12 to < 18 years of age at initial screening for the parent study. willing and able to give informed consent prior to substudy enrollment and to comply with extra study procedures. documented receipt of the 2 doses of the primary series of nvx-cov2373 and the booster (third dose) of nvx-cov2373 in the parent protocol. the booster dose must have been administered at least 6 months prior to entering the substudy. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile or postmenopausal) must agree to be heterosexually inactive from at least 28 days prior to entering and through the end of the substudy or agree to consistently use a medically acceptable method of contraception for the 28 days of follow-up for the substudy. is medically stable, as determined by the investigator (based on review of health status, vital signs (to include body temperature) and targeted physical examination (if medically indicated by reported symptoms). vital signs must be within medically acceptable ranges prior to administration of study vaccination. agree to not participate in any other non-nvx-cov2373 study during the substudy. note: for participants who develop covid-19, anti-sars-cov-2 therapy (approved, authorized or investigational) is permitted.

inclusion criteria: adult participants : each participant in the adult main study and/or the booster amendment must meet all of the following criteria to be enrolled in this study: adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars cov-2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile [i.e., 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination at the booster visit. pediatric participants : each participant in the pediatric expansion and/or the booster amendment must meet all of the following criteria to be enrolled in this study: pediatric participants 12 to < 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. agree to not participate in another sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination. each participant in the substudy must meet all of the following criteria to be enrolled in this study: be an active, enrolled participant in the 2019ncov-301 study. adults 18 years of age or older at initial screening for the parent study. willing and able to give informed consent prior to substudy enrollment and to comply with extra study procedures. documented receipt of the 2 doses of the primary series of nvx-cov2373 and the booster (third dose) of nvx-cov2373 in the parent protocol. the booster dose must have been administered at least 6 months prior to entering the substudy. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile or postmenopausal) must agree to be heterosexually inactive from at least 28 days prior to entering and through the end of the substudy or agree to consistently use a medically acceptable method of contraception for the 28 days of follow-up for the substudy. is medically stable, as determined by the investigator (based on review of health status, vital signs (to include body temperature) and targeted physical examination (if medically indicated by reported symptoms). vital signs must be within medically acceptable ranges prior to administration of study vaccination. agree to not participate in any other non-nvx-cov2373 study during the substudy. note: for participants who develop covid-19, anti-sars-cov-2 therapy (approved, authorized or investigational) is permitted.

inclusion criteria: adult participants : each participant in the adult main study and/or the booster amendment must meet all of the following criteria to be enrolled in this study: adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars cov-2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile [i.e., 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination at the booster visit. pediatric participants : each participant in the pediatric expansion and/or the booster amendment must meet all of the following criteria to be enrolled in this study: pediatric participants 12 to < 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. agree to not participate in another sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination. each participant in the substudy must meet all of the following criteria to be enrolled in this study: be an active, enrolled participant in the 2019ncov-301 study. adults 18 years of age or older at initial screening for the parent study. willing and able to give informed consent prior to substudy enrollment and to comply with extra study procedures. documented receipt of the 2 doses of the primary series of nvx-cov2373 and the booster (third dose) of nvx-cov2373 in the parent protocol. the booster dose must have been administered at least 6 months prior to entering the substudy. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile or postmenopausal) must agree to be heterosexually inactive from at least 28 days prior to entering and through the end of the substudy or agree to consistently use a medically acceptable method of contraception for the 28 days of follow-up for the substudy. is medically stable, as determined by the investigator (based on review of health status, vital signs (to include body temperature) and targeted physical examination (if medically indicated by reported symptoms). vital signs must be within medically acceptable ranges prior to administration of study vaccination. agree to not participate in any other non-nvx-cov2373 study during the substudy. note: for participants who develop covid-19, anti-sars-cov-2 therapy (approved, authorized or investigational) is permitted.

inclusion criteria: adult participants : each participant in the adult main study and/or the booster amendment must meet all of the following criteria to be enrolled in this study: adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars cov-2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile [i.e., 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing a valid documentation of vaccination at the booster visit. pediatric participants : each participant in the pediatric expansion and/or the booster amendment must meet all of the following criteria to be enrolled in this study: pediatric participants 12 to < 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. agree to not participate in another sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination.

inclusion criteria: adult participants : each participant in the adult main study and/or the booster amendment must meet all of the following criteria to be enrolled in this study: adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars cov-2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. participants of childbearing potential (defined as any participant who has experienced menarche and who is not surgically sterile [i.e., 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing a valid documentation of vaccination at the booster visit. pediatric participants : each participant in the pediatric expansion and/or the booster amendment must meet all of the following criteria to be enrolled in this study: pediatric participants 12 to < 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. agree to not participate in another sars-cov-2 prevention trial during the study follow-up. for the booster amendment only, active participants who received a full dose regimen of active vaccine (sars-cov-2 rs with matrix-m1 adjuvant) or any authorized/approved covid-19 vaccine are eligible for participation. such participants must demonstrate receipt by producing valid documentation of vaccination.

inclusion criteria: adult main study: adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars-cov-2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. pediatric expansion: pediatric participants 12 to < 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. agree to not participate in another sars-cov-2 prevention trial during the study follow-up

inclusion criteria: adult main study: adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars-cov-2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. pediatric expansion: pediatric participants 12 to < 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. agree to not participate in another sars-cov-2 prevention trial during the study follow-up

inclusion criteria: adult main study: 1. adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars-cov-2. 2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. 3. 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. pediatric expansion: 1. pediatric participants 12 to < 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. 2. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 3. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. agree to not participate in another sars-cov-2 prevention trial during the study follow-up

inclusion criteria: adult main study: 1. adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars-cov-2. 2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. 3. 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. pediatric expansion: 1. pediatric participants 12 to < 18 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. 2. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 3. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. agree to not participate in another sars-cov-2 prevention trial during the study follow-up

inclusion criteria: adult main study: 1. adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars-cov-2. 2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. 3. 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. pediatric expansion: 1. pediatric participants 12 to 17 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. 2. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 3. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. agree to not participate in another sars-cov-2 prevention trial during the study follow-up

inclusion criteria: adult main study: 1. adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars-cov-2. 2. willing and able to give informed consent prior to study enrollment and to comply with study procedures. 3. 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. is medically stable, as determined by the investigator (based on 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. agree to not participate in any other sars-cov-2 prevention trial during the study follow-up. pediatric expansion: 1. pediatric participants 12 to 17 years of age at screening, determined to be healthy or medically stable by the investigator (based on 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. 2. participant and parent(s)/caregiver(s) or legally acceptable representative willing and able to give informed consent and assent, as required, prior to study enrollment and to comply with study procedures. 3. 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] must agree to be heterosexually inactive from at least 28 days prior to enrollment and through 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. 4. agree to not participate in another sars-cov-2 prevention trial during the study follow-up

inclusion criteria: - adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars-cov-2. - willing and able to give informed consent prior to study enrollment and to comply with study procedures. - 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. - is medically stable, as determined by the investigator (based on 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. - agree to not participate in any other sars-cov-2 prevention trial during the study follow-up.

inclusion criteria: - adults ≥ 18 years of age at screening who, by virtue of age, race, ethnicity or life circumstances, are considered at substantial risk of exposure to and infection with sars-cov-2. - willing and able to give informed consent prior to study enrollment and to comply with study procedures. - 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 3 months after the last vaccination or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through 3 months after the last vaccination. - is medically stable, as determined by the investigator (based on 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. - agree to not participate in any other sars-cov-2 prevention trial during the study follow-up.