inclusion criteria for main cohort, vaccine declined group general and demographic criteria * age of 18 through 29 years. * ability and willingness to provide informed consent. * prefers not to receive covid-19 vaccine. * willingness to be followed for the planned duration of the study. * assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire with demonstration of understanding of all questionnaire items answered incorrectly. * access to device and internet for completion of study procedures. exclusion criteria for main cohort, vaccine declined group * prior administration of a coronavirus (sars-cov-2, sars-cov, mers-cov) vaccine or current/planned simultaneous participation in another interventional study to prevent or treat covid-19 (participation in studies of other investigational research agents allowed). * any medical, psychiatric, occupational, or other condition that, in the judgment of the investigator, would interfere with, or serve as a contraindication to, protocol adherence, or a volunteer's ability to give informed consent. inclusion criteria for prospective close contact (pcc) cohort * age of 18 years or older, at the time of signing the informed consent. * willing and able to provide informed consent. * expected to be in frequent close physical proximity with main cohort participant during the study. * willing to share results of sars-cov-2 testing. * access to device and internet for completion of study procedures inclusion criteria for case-ascertained close contact (cacc) cohort * age of 18 years or older, at the time of signing the informed consent. * willing and able to provide informed consent. * access to device and internet for completion of study procedures. * willing to share results of sars-cov-2 testing. * had close contact with main cohort participant with known pcr-confirmed sars-cov-2 infection (eg, index case). close contacts will have had exposure to the index participant, generally within 72 hours of an index diagnosis, and may include individuals that meet any of the following guidelines: prolonged close physical proximity with main cohort participant within a residence/vehicle/enclosed space without maintaining social distance, medical staff, first responders, or other care persons who cared for the index case without appropriate personal protective equipment. further information on the definition of close contact can be found in the covpn 3006 study specific procedures (ssp).

inclusion criteria for main cohort, vaccine declined group general and demographic criteria * age of 18 through 29 years. * ability and willingness to provide informed consent. * prefers not to receive covid-19 vaccine. * willingness to be followed for the planned duration of the study. * assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire with demonstration of understanding of all questionnaire items answered incorrectly. * access to device and internet for completion of study procedures. exclusion criteria for main cohort, vaccine declined group * prior administration of a coronavirus (sars-cov-2, sars-cov, mers-cov) vaccine or current/planned simultaneous participation in another interventional study to prevent or treat covid-19 (participation in studies of other investigational research agents allowed). * any medical, psychiatric, occupational, or other condition that, in the judgment of the investigator, would interfere with, or serve as a contraindication to, protocol adherence, or a volunteer's ability to give informed consent. inclusion criteria for prospective close contact (pcc) cohort * age of 18 years or older, at the time of signing the informed consent. * willing and able to provide informed consent. * expected to be in frequent close physical proximity with main cohort participant during the study. * willing to share results of sars-cov-2 testing. * access to device and internet for completion of study procedures inclusion criteria for case-ascertained close contact (cacc) cohort * age of 18 years or older, at the time of signing the informed consent. * willing and able to provide informed consent. * access to device and internet for completion of study procedures. * willing to share results of sars-cov-2 testing. * had close contact with main cohort participant with known pcr-confirmed sars-cov-2 infection (eg, index case). close contacts will have had exposure to the index participant, generally within 72 hours of an index diagnosis, and may include individuals that meet any of the following guidelines: prolonged close physical proximity with main cohort participant within a residence/vehicle/enclosed space without maintaining social distance, medical staff, first responders, or other care persons who cared for the index case without appropriate personal protective equipment. further information on the definition of close contact can be found in the covpn 3006 study specific procedures (ssp).

inclusion criteria for main cohort, vaccine declined group general and demographic criteria age of 18 through 29 years. ability and willingness to provide informed consent. prefers not to receive covid-19 vaccine. willingness to be followed for the planned duration of the study. assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire with demonstration of understanding of all questionnaire items answered incorrectly. access to device and internet for completion of study procedures. exclusion criteria for main cohort, vaccine declined group prior administration of a coronavirus (sars-cov-2, sars-cov, mers-cov) vaccine or current/planned simultaneous participation in another interventional study to prevent or treat covid-19 (participation in studies of other investigational research agents allowed). any medical, psychiatric, occupational, or other condition that, in the judgment of the investigator, would interfere with, or serve as a contraindication to, protocol adherence, or a volunteer's ability to give informed consent. inclusion criteria for prospective close contact (pcc) cohort age of 18 years or older, at the time of signing the informed consent. willing and able to provide informed consent. expected to be in frequent close physical proximity with main cohort participant during the study. willing to share results of sars-cov-2 testing. access to device and internet for completion of study procedures inclusion criteria for case-ascertained close contact (cacc) cohort age of 18 years or older, at the time of signing the informed consent. willing and able to provide informed consent. access to device and internet for completion of study procedures. willing to share results of sars-cov-2 testing. had close contact with main cohort participant with known pcr-confirmed sars-cov-2 infection (eg, index case). close contacts will have had exposure to the index participant, generally within 72 hours of an index diagnosis, and may include individuals that meet any of the following guidelines: prolonged close physical proximity with main cohort participant within a residence/vehicle/enclosed space without maintaining social distance, medical staff, first responders, or other care persons who cared for the index case without appropriate personal protective equipment. further information on the definition of close contact can be found in the covpn 3006 study specific procedures (ssp).

inclusion criteria for main cohort, vaccine declined group general and demographic criteria age of 18 through 29 years. ability and willingness to provide informed consent. prefers not to receive covid-19 vaccine. willingness to be followed for the planned duration of the study. assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire with demonstration of understanding of all questionnaire items answered incorrectly. access to device and internet for completion of study procedures. exclusion criteria for main cohort, vaccine declined group prior administration of a coronavirus (sars-cov-2, sars-cov, mers-cov) vaccine or current/planned simultaneous participation in another interventional study to prevent or treat covid-19 (participation in studies of other investigational research agents allowed). any medical, psychiatric, occupational, or other condition that, in the judgment of the investigator, would interfere with, or serve as a contraindication to, protocol adherence, or a volunteer's ability to give informed consent. inclusion criteria for prospective close contact (pcc) cohort age of 18 years or older, at the time of signing the informed consent. willing and able to provide informed consent. expected to be in frequent close physical proximity with main cohort participant during the study. willing to share results of sars-cov-2 testing. access to device and internet for completion of study procedures inclusion criteria for case-ascertained close contact (cacc) cohort age of 18 years or older, at the time of signing the informed consent. willing and able to provide informed consent. access to device and internet for completion of study procedures. willing to share results of sars-cov-2 testing. had close contact with main cohort participant with known pcr-confirmed sars-cov-2 infection (eg, index case). close contacts will have had exposure to the index participant, generally within 72 hours of an index diagnosis, and may include individuals that meet any of the following guidelines: prolonged close physical proximity with main cohort participant within a residence/vehicle/enclosed space without maintaining social distance, medical staff, first responders, or other care persons who cared for the index case without appropriate personal protective equipment. further information on the definition of close contact can be found in the covpn 3006 study specific procedures (ssp).

inclusion criteria for immediate vaccination and standard of care groups: - willingness to be followed for the planned duration of the study. - agrees to allow study staff to access school sars-cov-2 testing data and outcomes, if applicable. - ability and willingness to provide informed consent. - assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire with demonstration of understanding of all questionnaire items answered incorrectly. - willing to be randomized to either immediate vaccination or standard of care group and comply with planned study procedures - agrees not to enroll in another study of an investigational research agent until the end of the study. - access to device and internet for completion of study procedures. exclusion criteria for immediate vaccination and standard of care groups: - acutely ill 72 hours prior to or at screening. volunteers meeting this criterion may be rescheduled within the relevant window periods. participants with minor illnesses can be enrolled at the discretion of the investigator. - blood products, systemic immunoglobulins, or monoclonal antibodies (including against sars-cov-2) received within 90 days before first vaccination. - investigational research agents received within 30 days before first vaccination. - self-reported known history of sars-cov-2 infection. - prefers to receive covid-19 vaccination immediately, (these volunteers to be referred to community resources for vaccination). - prior administration of a coronavirus (sars-cov-2, sars-cov, mers-cov) vaccine or current/planned simultaneous participation in another interventional study to prevent or treat covid-19. - immunosuppressive medications received within 168 days before first vaccination (not exclusionary: [1] corticosteroid nasal spray; [2] inhaled corticosteroids; [3] topical corticosteroids for mild, uncomplicated dermatologic condition; or [4] a single course of oral/parenteral prednisone or equivalent at doses < 60 mg/day and length of therapy < 11 days with completion at least 30 days prior to enrollment). - clinically significant medical condition, physical examination findings, or past medical history with clinically significant implications for current health. a clinically significant condition or process includes but is not limited to a process that would affect the immune response (well-controlled human immunodeficiency virus infection is allowed), or any condition specifically listed among the exclusion criteria below. - any medical, psychiatric, occupational, or other condition that, in the judgment of the investigator, would interfere with, or serve as a contraindication to, protocol adherence, assessment of safety or reactogenicity, or a volunteer's ability to give informed consent. - bleeding disorder (eg, factor deficiency, coagulopathy, or platelet disorder requiring special precautions). - asplenia: any condition resulting in the absence of a functional spleen. - history of angioedema or anaphylaxis, including to vaccines or vaccine components (not exclusionary: angioedema or anaphylaxis with known trigger and no episodes within five years.). - history of generalized urticaria within past five years. inclusion criteria for vaccine declined group: - ability and willingness to provide informed consent. - prefers not to receive covid-19 vaccine. - willingness to be followed for the planned duration of the study. - assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire with demonstration of understanding of all questionnaire items answered incorrectly. - access to device and internet for completion of study procedures. exclusion criteria for vaccine declined group: - prior administration of a coronavirus (sars-cov-2, sars-cov, mers-cov) vaccine or current/planned simultaneous participation in another interventional study to prevent or treat covid-19 (participation in studies of other investigational research agents allowed). - any medical, psychiatric, occupational, or other condition that, in the judgment of the investigator, would interfere with, or serve as a contraindication to, protocol adherence, or a volunteer's ability to give informed consent.

inclusion criteria for immediate vaccination and standard of care groups: - willingness to be followed for the planned duration of the study. - agrees to allow study staff to access school sars-cov-2 testing data and outcomes, if applicable. - ability and willingness to provide informed consent. - assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire with demonstration of understanding of all questionnaire items answered incorrectly. - willing to be randomized to either immediate vaccination or standard of care group and comply with planned study procedures - agrees not to enroll in another study of an investigational research agent until the end of the study. - access to device and internet for completion of study procedures. exclusion criteria for immediate vaccination and standard of care groups: - acutely ill 72 hours prior to or at screening. volunteers meeting this criterion may be rescheduled within the relevant window periods. participants with minor illnesses can be enrolled at the discretion of the investigator. - blood products, systemic immunoglobulins, or monoclonal antibodies (including against sars-cov-2) received within 90 days before first vaccination. - investigational research agents received within 30 days before first vaccination. - self-reported known history of sars-cov-2 infection. - prefers to receive covid-19 vaccination immediately, (these volunteers to be referred to community resources for vaccination). - prior administration of a coronavirus (sars-cov-2, sars-cov, mers-cov) vaccine or current/planned simultaneous participation in another interventional study to prevent or treat covid-19. - immunosuppressive medications received within 168 days before first vaccination (not exclusionary: [1] corticosteroid nasal spray; [2] inhaled corticosteroids; [3] topical corticosteroids for mild, uncomplicated dermatologic condition; or [4] a single course of oral/parenteral prednisone or equivalent at doses < 60 mg/day and length of therapy < 11 days with completion at least 30 days prior to enrollment). - clinically significant medical condition, physical examination findings, or past medical history with clinically significant implications for current health. a clinically significant condition or process includes but is not limited to a process that would affect the immune response (well-controlled human immunodeficiency virus infection is allowed), or any condition specifically listed among the exclusion criteria below. - any medical, psychiatric, occupational, or other condition that, in the judgment of the investigator, would interfere with, or serve as a contraindication to, protocol adherence, assessment of safety or reactogenicity, or a volunteer's ability to give informed consent. - bleeding disorder (eg, factor deficiency, coagulopathy, or platelet disorder requiring special precautions). - asplenia: any condition resulting in the absence of a functional spleen. - history of angioedema or anaphylaxis, including to vaccines or vaccine components (not exclusionary: angioedema or anaphylaxis with known trigger and no episodes within five years.). - history of generalized urticaria within past five years. inclusion criteria for vaccine declined group: - ability and willingness to provide informed consent. - prefers not to receive covid-19 vaccine. - willingness to be followed for the planned duration of the study. - assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire with demonstration of understanding of all questionnaire items answered incorrectly. - access to device and internet for completion of study procedures. exclusion criteria for vaccine declined group: - prior administration of a coronavirus (sars-cov-2, sars-cov, mers-cov) vaccine or current/planned simultaneous participation in another interventional study to prevent or treat covid-19 (participation in studies of other investigational research agents allowed). - any medical, psychiatric, occupational, or other condition that, in the judgment of the investigator, would interfere with, or serve as a contraindication to, protocol adherence, or a volunteer's ability to give informed consent.

inclusion criteria: - enrollment in a post-secondary educational institution and willingness to be followed for the planned duration of the study. - agrees to allow study staff to access school sars-cov-2 testing data and outcomes. - ability and willingness to provide informed consent. - assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire prior to first vaccination with demonstration of understanding of all questionnaire items answered incorrectly. - willing to be randomized to either immediate or delayed vaccination group and comply with planned study procedures - agrees not to enroll in another study of an investigational research agent until the end of the study. - access to device and internet for telehealth visits.

inclusion criteria: - enrollment in a post-secondary educational institution and willingness to be followed for the planned duration of the study. - agrees to allow study staff to access school sars-cov-2 testing data and outcomes. - ability and willingness to provide informed consent. - assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire prior to first vaccination with demonstration of understanding of all questionnaire items answered incorrectly. - willing to be randomized to either immediate or delayed vaccination group and comply with planned study procedures - agrees not to enroll in another study of an investigational research agent until the end of the study. - access to device and internet for telehealth visits.

inclusion criteria: - enrollment in a participating university and willingness to be followed for the planned duration of the study. - agrees to allow study staff to access university sars-cov-2 testing data and outcomes. - ability and willingness to provide informed consent. - assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire prior to first vaccination with demonstration of understanding of all questionnaire items answered incorrectly. - willing to defer sars-cov-2 licensed or eua vaccine until visit 6 (month 4) - agrees not to enroll in another study of an investigational research agent until the end of the study. - access to device and internet for telehealth visits.

inclusion criteria: - enrollment in a participating university and willingness to be followed for the planned duration of the study. - agrees to allow study staff to access university sars-cov-2 testing data and outcomes. - ability and willingness to provide informed consent. - assessment of understanding: volunteer demonstrates understanding of this study; completes a questionnaire prior to first vaccination with demonstration of understanding of all questionnaire items answered incorrectly. - willing to defer sars-cov-2 licensed or eua vaccine until visit 6 (month 4) - agrees not to enroll in another study of an investigational research agent until the end of the study. - access to device and internet for telehealth visits.