inclusion criteria: to be included in this study, each individual must satisfy all the following criteria: 1. adults 18 to 49 years (inclusive) of age at the time of vaccination in study 307 who received two or three doses of mrna prior to enrollment in study 307, then one dose of ancestral strain nvx-cov2373 in study 307. 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 the end of study (eos) visit or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through the eos visit. 4. is medically stable, as determined by the investigator (based on review of health status, vital signs \[to include body temperature\], medical history, and physical examination \[to include body weight\]). vital signs must be within medically acceptable ranges prior to the study vaccination. 5. agree to not participate in any other sars-cov-2 prevention or treatment trials for the duration of the study. note: for participants who become hospitalized with covid-19, participation in investigational treatment studies is permitted. 6. documented receipt of covid-19 vaccines. the most recent dose of nvx-cov2373 must have been administered at least 180 days prior to vaccination in this study.

inclusion criteria: to be included in this study, each individual must satisfy all the following criteria: 1. adults 18 to 49 years (inclusive) of age at the time of vaccination in study 307 who received two or three doses of mrna prior to enrollment in study 307, then one dose of ancestral strain nvx-cov2373 in study 307. 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 the end of study (eos) visit or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through the eos visit. 4. is medically stable, as determined by the investigator (based on review of health status, vital signs \[to include body temperature\], medical history, and physical examination \[to include body weight\]). vital signs must be within medically acceptable ranges prior to the study vaccination. 5. agree to not participate in any other sars-cov-2 prevention or treatment trials for the duration of the study. note: for participants who become hospitalized with covid-19, participation in investigational treatment studies is permitted. 6. documented receipt of covid-19 vaccines. the most recent dose of nvx-cov2373 must have been administered at least 180 days prior to vaccination in this study.

inclusion criteria: to be included in this study, each individual must satisfy all the following criteria: adults 18 to 49 years (inclusive) of age at the time of vaccination in study 307 who received two or three doses of mrna prior to enrollment in study 307, then one dose of ancestral strain nvx-cov2373 in study 307. 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 the end of study (eos) visit or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through the eos visit. is medically stable, as determined by the investigator (based on review of health status, vital signs [to include body temperature], medical history, and physical examination [to include body weight]). vital signs must be within medically acceptable ranges prior to the study vaccination. agree to not participate in any other sars-cov-2 prevention or treatment trials for the duration of the study. note: for participants who become hospitalized with covid-19, participation in investigational treatment studies is permitted. documented receipt of covid-19 vaccines. the most recent dose of nvx-cov2373 must have been administered at least 180 days prior to vaccination in this study.

inclusion criteria: to be included in this study, each individual must satisfy all the following criteria: adults 18 to 49 years (inclusive) of age at the time of vaccination in study 307 who received two or three doses of mrna prior to enrollment in study 307, then one dose of ancestral strain nvx-cov2373 in study 307. 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 the end of study (eos) visit or agree to consistently use a medically acceptable method of contraception from at least 28 days prior to enrollment and through the eos visit. is medically stable, as determined by the investigator (based on review of health status, vital signs [to include body temperature], medical history, and physical examination [to include body weight]). vital signs must be within medically acceptable ranges prior to the study vaccination. agree to not participate in any other sars-cov-2 prevention or treatment trials for the duration of the study. note: for participants who become hospitalized with covid-19, participation in investigational treatment studies is permitted. documented receipt of covid-19 vaccines. the most recent dose of nvx-cov2373 must have been administered at least 180 days prior to vaccination in this study.