a subject who meets any of the following criteria will be excluded from participation in this study: 1. positive pregnancy test either at screening or just prior to each vaccine administration. 2. female subject who is breastfeeding or plans to breastfeed from the time of the first vaccination through 60 days after the last vaccination. 3. has any medical disease or condition that, in the opinion of the participating site principal investigator (pi) or appropriate sub-investigator, precludes study participation.\* \*including acute, subacute, intermittent or chronic medical disease or condition that would place the subject at an unacceptable risk of injury, render the subject unable to meet the requirements of the protocol, or may interfere with the evaluation of responses or the subject's successful completion of this trial. 4. presence of self-reported or medically documented significant medical or psychiatric condition(s).\* \*significant medical or psychiatric conditions include but are not limited to: respiratory disease (e.g., chronic obstructive pulmonary disease \[copd\], asthma) requiring daily medications currently or any treatment of respiratory disease exacerbations (e.g., asthma exacerbation) in the last 5 years. asthma medications: inhaled, oral, or intravenous (iv) corticosteroids, leukotriene modifiers, long and short acting beta agonists, theophylline, ipratropium, biologics. significant cardiovascular disease (e.g., congestive heart failure, cardiomyopathy, ischemic heart disease), history of myocarditis or pericarditis as an adult, myocardial infarction (mi) within past 6 months, coronary artery bypass surgery or stent placement, or uncontrolled cardiac arrhythmia. neurological or neurodevelopmental conditions (e.g., history of migraines in the past 5 years, epilepsy, stroke, seizures in the last 3 years, encephalopathy, focal neurologic deficits, guillain-barré syndrome, encephalomyelitis, transverse myelitis, stroke or transient ischemic attack, multiple sclerosis, parkinson's disease, amyotrophic lateral sclerosis, creutzfeldt-jakob disease, or alzheimer's disease). ongoing malignancy or recent diagnosis of malignancy in the last five years excluding basal cell and squamous cell carcinoma of the skin, which are allowed. an autoimmune disease, including hypothyroidism without a defined non-autoimmune cause, localized or history of psoriasis. an immunodeficiency of any cause. chronic kidney disease, estimated glomerular filtration rate (egfr) \<60 ml/min/1.73m\^2. 5. has an acute illness\*, as determined by the participating site pi or appropriate sub-investigator, with or without fever \[oral temperature \>/= 38.0 degrees celsius (100.4 degrees fahrenheit)\] within 72 hours prior to each vaccination. \*an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the participating site pi or appropriate sub-investigator, the residual symptoms will not interfere with the ability to assess safety parameters as required by the protocol. 6. has a positive test result for hepatitis b surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) types 1 or 2 antibodies at screening. 7. has participated in another investigational study involving any investigational product\* within 60 days, or 5 half-lives, whichever is longer, before the first vaccine administration. \*study drug, biologic or device 8. currently enrolled in or plans to participate in another clinical trial with an investigational agent\* that will be received during the study-reporting period.\*\* \*including licensed or unlicensed vaccine, drug, biologic, device, blood product, or medication. \*\*13 months after the first vaccination. 9. has previously participated in an investigational study involving lipid nanoparticles (lnps) (a component of the investigational vaccine assessed in this trial). 10. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to any previous licensed or unlicensed vaccines. 11. chronic use (more than 14 continuous days) of any medications that may be associated with impaired immune responsiveness.\* \*including, but not limited to, systemic corticosteroids exceeding 10 mg/day of prednisone equivalent, allergy injections, immunoglobulin, interferon, immunomodulators, cytotoxic drugs, or other similar or toxic drugs during the preceding 6-month period prior to vaccine administration (day 1). the use of low dose topical, ophthalmic, inhaled and intranasal steroid preparations will be permitted. 12. anticipating the need for immunosuppressive treatment within the next 6 months. 13. received immunoglobulins and/or any blood or blood products within the 4 months before the first vaccine administration or at any time during the study. 14. has any blood dyscrasias or significant disorder of coagulation. 15. has any chronic liver disease, including fatty liver. 16. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 6 months before the first vaccine administration. 17. has a positive test result for drugs of abuse at screening or before the first vaccine administration. if cannabis is the only detected drug, inclusion is permitted. 18. has any abnormality or permanent body art (e.g., tattoo) that would interfere with the ability to observe local reactions at the injection site (deltoid region). 19. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 20. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 21. receipt of any other sars-cov-2 or other experimental coronavirus vaccine at any time prior to or during the study. 22. close contact of anyone known to have sars-cov-2 infection within 30 days prior to vaccine administration. 23. history of covid-19 diagnosis. 24. on current treatment with investigational agents for prophylaxis of covid-19. 25. current use of any prescription or over-the-counter medications within 7 days prior to vaccination, unless approved by the investigator or necessary to manage a chronic condition. 26. plan to travel outside the united states (us) (continental us, hawaii, and alaska) from enrollment through 28 days after the last vaccination. 27. reside in a nursing home or other skilled nursing facility or have a requirement for skilled nursing care. 28. non-ambulatory. 29. for subjects \>/= 56 years of age, history of chronic smoking within the prior year. 30. for subjects \>/= 56 years of age, current smoking or vaping. 31. for subjects \>/= 56 years of age, individuals currently working with high risk of exposure to sars-cov-2 (e.g., active health care workers with direct patient contact, emergency response personnel). optional substudy

a subject who meets any of the following criteria will be excluded from participation in this study: 1. positive pregnancy test either at screening or just prior to each vaccine administration. 2. female subject who is breastfeeding or plans to breastfeed from the time of the first vaccination through 60 days after the last vaccination. 3. has any medical disease or condition that, in the opinion of the participating site principal investigator (pi) or appropriate sub-investigator, precludes study participation.\* \*including acute, subacute, intermittent or chronic medical disease or condition that would place the subject at an unacceptable risk of injury, render the subject unable to meet the requirements of the protocol, or may interfere with the evaluation of responses or the subject's successful completion of this trial. 4. presence of self-reported or medically documented significant medical or psychiatric condition(s).\* \*significant medical or psychiatric conditions include but are not limited to: respiratory disease (e.g., chronic obstructive pulmonary disease \[copd\], asthma) requiring daily medications currently or any treatment of respiratory disease exacerbations (e.g., asthma exacerbation) in the last 5 years. asthma medications: inhaled, oral, or intravenous (iv) corticosteroids, leukotriene modifiers, long and short acting beta agonists, theophylline, ipratropium, biologics. significant cardiovascular disease (e.g., congestive heart failure, cardiomyopathy, ischemic heart disease), history of myocarditis or pericarditis as an adult, myocardial infarction (mi) within past 6 months, coronary artery bypass surgery or stent placement, or uncontrolled cardiac arrhythmia. neurological or neurodevelopmental conditions (e.g., history of migraines in the past 5 years, epilepsy, stroke, seizures in the last 3 years, encephalopathy, focal neurologic deficits, guillain-barré syndrome, encephalomyelitis, transverse myelitis, stroke or transient ischemic attack, multiple sclerosis, parkinson's disease, amyotrophic lateral sclerosis, creutzfeldt-jakob disease, or alzheimer's disease). ongoing malignancy or recent diagnosis of malignancy in the last five years excluding basal cell and squamous cell carcinoma of the skin, which are allowed. an autoimmune disease, including hypothyroidism without a defined non-autoimmune cause, localized or history of psoriasis. an immunodeficiency of any cause. chronic kidney disease, estimated glomerular filtration rate (egfr) \<60 ml/min/1.73m\^2. 5. has an acute illness\*, as determined by the participating site pi or appropriate sub-investigator, with or without fever \[oral temperature \>/= 38.0 degrees celsius (100.4 degrees fahrenheit)\] within 72 hours prior to each vaccination. \*an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the participating site pi or appropriate sub-investigator, the residual symptoms will not interfere with the ability to assess safety parameters as required by the protocol. 6. has a positive test result for hepatitis b surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) types 1 or 2 antibodies at screening. 7. has participated in another investigational study involving any investigational product\* within 60 days, or 5 half-lives, whichever is longer, before the first vaccine administration. \*study drug, biologic or device 8. currently enrolled in or plans to participate in another clinical trial with an investigational agent\* that will be received during the study-reporting period.\*\* \*including licensed or unlicensed vaccine, drug, biologic, device, blood product, or medication. \*\*13 months after the first vaccination. 9. has previously participated in an investigational study involving lipid nanoparticles (lnps) (a component of the investigational vaccine assessed in this trial). 10. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to any previous licensed or unlicensed vaccines. 11. chronic use (more than 14 continuous days) of any medications that may be associated with impaired immune responsiveness.\* \*including, but not limited to, systemic corticosteroids exceeding 10 mg/day of prednisone equivalent, allergy injections, immunoglobulin, interferon, immunomodulators, cytotoxic drugs, or other similar or toxic drugs during the preceding 6-month period prior to vaccine administration (day 1). the use of low dose topical, ophthalmic, inhaled and intranasal steroid preparations will be permitted. 12. anticipating the need for immunosuppressive treatment within the next 6 months. 13. received immunoglobulins and/or any blood or blood products within the 4 months before the first vaccine administration or at any time during the study. 14. has any blood dyscrasias or significant disorder of coagulation. 15. has any chronic liver disease, including fatty liver. 16. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 6 months before the first vaccine administration. 17. has a positive test result for drugs of abuse at screening or before the first vaccine administration. if cannabis is the only detected drug, inclusion is permitted. 18. has any abnormality or permanent body art (e.g., tattoo) that would interfere with the ability to observe local reactions at the injection site (deltoid region). 19. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 20. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 21. receipt of any other sars-cov-2 or other experimental coronavirus vaccine at any time prior to or during the study. 22. close contact of anyone known to have sars-cov-2 infection within 30 days prior to vaccine administration. 23. history of covid-19 diagnosis. 24. on current treatment with investigational agents for prophylaxis of covid-19. 25. current use of any prescription or over-the-counter medications within 7 days prior to vaccination, unless approved by the investigator or necessary to manage a chronic condition. 26. plan to travel outside the united states (us) (continental us, hawaii, and alaska) from enrollment through 28 days after the last vaccination. 27. reside in a nursing home or other skilled nursing facility or have a requirement for skilled nursing care. 28. non-ambulatory. 29. for subjects \>/= 56 years of age, history of chronic smoking within the prior year. 30. for subjects \>/= 56 years of age, current smoking or vaping. 31. for subjects \>/= 56 years of age, individuals currently working with high risk of exposure to sars-cov-2 (e.g., active health care workers with direct patient contact, emergency response personnel). optional substudy

a subject who meets any of the following criteria will be excluded from participation in this study: positive pregnancy test either at screening or just prior to each vaccine administration. female subject who is breastfeeding or plans to breastfeed from the time of the first vaccination through 60 days after the last vaccination. has any medical disease or condition that, in the opinion of the participating site principal investigator (pi) or appropriate sub-investigator, precludes study participation.* *including acute, subacute, intermittent or chronic medical disease or condition that would place the subject at an unacceptable risk of injury, render the subject unable to meet the requirements of the protocol, or may interfere with the evaluation of responses or the subject's successful completion of this trial. presence of self-reported or medically documented significant medical or psychiatric condition(s).* *significant medical or psychiatric conditions include but are not limited to: respiratory disease (e.g., chronic obstructive pulmonary disease [copd], asthma) requiring daily medications currently or any treatment of respiratory disease exacerbations (e.g., asthma exacerbation) in the last 5 years. asthma medications: inhaled, oral, or intravenous (iv) corticosteroids, leukotriene modifiers, long and short acting beta agonists, theophylline, ipratropium, biologics. significant cardiovascular disease (e.g., congestive heart failure, cardiomyopathy, ischemic heart disease), history of myocarditis or pericarditis as an adult, myocardial infarction (mi) within past 6 months, coronary artery bypass surgery or stent placement, or uncontrolled cardiac arrhythmia. neurological or neurodevelopmental conditions (e.g., history of migraines in the past 5 years, epilepsy, stroke, seizures in the last 3 years, encephalopathy, focal neurologic deficits, guillain-barré syndrome, encephalomyelitis, transverse myelitis, stroke or transient ischemic attack, multiple sclerosis, parkinson's disease, amyotrophic lateral sclerosis, creutzfeldt-jakob disease, or alzheimer's disease). ongoing malignancy or recent diagnosis of malignancy in the last five years excluding basal cell and squamous cell carcinoma of the skin, which are allowed. an autoimmune disease, including hypothyroidism without a defined non-autoimmune cause, localized or history of psoriasis. an immunodeficiency of any cause. chronic kidney disease, estimated glomerular filtration rate (egfr) <60 ml/min/1.73m^2. has an acute illness*, as determined by the participating site pi or appropriate sub-investigator, with or without fever [oral temperature >/= 38.0 degrees celsius (100.4 degrees fahrenheit)] within 72 hours prior to each vaccination. *an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the participating site pi or appropriate sub-investigator, the residual symptoms will not interfere with the ability to assess safety parameters as required by the protocol. has a positive test result for hepatitis b surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) types 1 or 2 antibodies at screening. has participated in another investigational study involving any investigational product* within 60 days, or 5 half-lives, whichever is longer, before the first vaccine administration. *study drug, biologic or device currently enrolled in or plans to participate in another clinical trial with an investigational agent* that will be received during the study-reporting period.** *including licensed or unlicensed vaccine, drug, biologic, device, blood product, or medication. **13 months after the first vaccination. has previously participated in an investigational study involving lipid nanoparticles (lnps) (a component of the investigational vaccine assessed in this trial). has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to any previous licensed or unlicensed vaccines. chronic use (more than 14 continuous days) of any medications that may be associated with impaired immune responsiveness.* *including, but not limited to, systemic corticosteroids exceeding 10 mg/day of prednisone equivalent, allergy injections, immunoglobulin, interferon, immunomodulators, cytotoxic drugs, or other similar or toxic drugs during the preceding 6-month period prior to vaccine administration (day 1). the use of low dose topical, ophthalmic, inhaled and intranasal steroid preparations will be permitted. anticipating the need for immunosuppressive treatment within the next 6 months. received immunoglobulins and/or any blood or blood products within the 4 months before the first vaccine administration or at any time during the study. has any blood dyscrasias or significant disorder of coagulation. has any chronic liver disease, including fatty liver. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 6 months before the first vaccine administration. has a positive test result for drugs of abuse at screening or before the first vaccine administration. if cannabis is the only detected drug, inclusion is permitted. has any abnormality or permanent body art (e.g., tattoo) that would interfere with the ability to observe local reactions at the injection site (deltoid region). received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. receipt of any other sars-cov-2 or other experimental coronavirus vaccine at any time prior to or during the study. close contact of anyone known to have sars-cov-2 infection within 30 days prior to vaccine administration. history of covid-19 diagnosis. on current treatment with investigational agents for prophylaxis of covid-19. current use of any prescription or over-the-counter medications within 7 days prior to vaccination, unless approved by the investigator or necessary to manage a chronic condition. plan to travel outside the united states (us) (continental us, hawaii, and alaska) from enrollment through 28 days after the last vaccination. reside in a nursing home or other skilled nursing facility or have a requirement for skilled nursing care. non-ambulatory. for subjects >/= 56 years of age, history of chronic smoking within the prior year. for subjects >/= 56 years of age, current smoking or vaping. for subjects >/= 56 years of age, individuals currently working with high risk of exposure to sars-cov-2 (e.g., active health care workers with direct patient contact, emergency response personnel). optional substudy

a subject who meets any of the following criteria will be excluded from participation in this study: positive pregnancy test either at screening or just prior to each vaccine administration. female subject who is breastfeeding or plans to breastfeed from the time of the first vaccination through 60 days after the last vaccination. has any medical disease or condition that, in the opinion of the participating site principal investigator (pi) or appropriate sub-investigator, precludes study participation.* *including acute, subacute, intermittent or chronic medical disease or condition that would place the subject at an unacceptable risk of injury, render the subject unable to meet the requirements of the protocol, or may interfere with the evaluation of responses or the subject's successful completion of this trial. presence of self-reported or medically documented significant medical or psychiatric condition(s).* *significant medical or psychiatric conditions include but are not limited to: respiratory disease (e.g., chronic obstructive pulmonary disease [copd], asthma) requiring daily medications currently or any treatment of respiratory disease exacerbations (e.g., asthma exacerbation) in the last 5 years. asthma medications: inhaled, oral, or intravenous (iv) corticosteroids, leukotriene modifiers, long and short acting beta agonists, theophylline, ipratropium, biologics. significant cardiovascular disease (e.g., congestive heart failure, cardiomyopathy, ischemic heart disease), history of myocarditis or pericarditis as an adult, myocardial infarction (mi) within past 6 months, coronary artery bypass surgery or stent placement, or uncontrolled cardiac arrhythmia. neurological or neurodevelopmental conditions (e.g., history of migraines in the past 5 years, epilepsy, stroke, seizures in the last 3 years, encephalopathy, focal neurologic deficits, guillain-barré syndrome, encephalomyelitis, transverse myelitis, stroke or transient ischemic attack, multiple sclerosis, parkinson's disease, amyotrophic lateral sclerosis, creutzfeldt-jakob disease, or alzheimer's disease). ongoing malignancy or recent diagnosis of malignancy in the last five years excluding basal cell and squamous cell carcinoma of the skin, which are allowed. an autoimmune disease, including hypothyroidism without a defined non-autoimmune cause, localized or history of psoriasis. an immunodeficiency of any cause. chronic kidney disease, estimated glomerular filtration rate (egfr) <60 ml/min/1.73m^2. has an acute illness*, as determined by the participating site pi or appropriate sub-investigator, with or without fever [oral temperature >/= 38.0 degrees celsius (100.4 degrees fahrenheit)] within 72 hours prior to each vaccination. *an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the participating site pi or appropriate sub-investigator, the residual symptoms will not interfere with the ability to assess safety parameters as required by the protocol. has a positive test result for hepatitis b surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) types 1 or 2 antibodies at screening. has participated in another investigational study involving any investigational product* within 60 days, or 5 half-lives, whichever is longer, before the first vaccine administration. *study drug, biologic or device currently enrolled in or plans to participate in another clinical trial with an investigational agent* that will be received during the study-reporting period.** *including licensed or unlicensed vaccine, drug, biologic, device, blood product, or medication. **13 months after the first vaccination. has previously participated in an investigational study involving lipid nanoparticles (lnps) (a component of the investigational vaccine assessed in this trial). has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to any previous licensed or unlicensed vaccines. chronic use (more than 14 continuous days) of any medications that may be associated with impaired immune responsiveness.* *including, but not limited to, systemic corticosteroids exceeding 10 mg/day of prednisone equivalent, allergy injections, immunoglobulin, interferon, immunomodulators, cytotoxic drugs, or other similar or toxic drugs during the preceding 6-month period prior to vaccine administration (day 1). the use of low dose topical, ophthalmic, inhaled and intranasal steroid preparations will be permitted. anticipating the need for immunosuppressive treatment within the next 6 months. received immunoglobulins and/or any blood or blood products within the 4 months before the first vaccine administration or at any time during the study. has any blood dyscrasias or significant disorder of coagulation. has any chronic liver disease, including fatty liver. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 6 months before the first vaccine administration. has a positive test result for drugs of abuse at screening or before the first vaccine administration. if cannabis is the only detected drug, inclusion is permitted. has any abnormality or permanent body art (e.g., tattoo) that would interfere with the ability to observe local reactions at the injection site (deltoid region). received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. receipt of any other sars-cov-2 or other experimental coronavirus vaccine at any time prior to or during the study. close contact of anyone known to have sars-cov-2 infection within 30 days prior to vaccine administration. history of covid-19 diagnosis. on current treatment with investigational agents for prophylaxis of covid-19. current use of any prescription or over-the-counter medications within 7 days prior to vaccination, unless approved by the investigator or necessary to manage a chronic condition. plan to travel outside the united states (us) (continental us, hawaii, and alaska) from enrollment through 28 days after the last vaccination. reside in a nursing home or other skilled nursing facility or have a requirement for skilled nursing care. non-ambulatory. for subjects >/= 56 years of age, history of chronic smoking within the prior year. for subjects >/= 56 years of age, current smoking or vaping. for subjects >/= 56 years of age, individuals currently working with high risk of exposure to sars-cov-2 (e.g., active health care workers with direct patient contact, emergency response personnel). optional substudy

a subject who meets any of the following criteria will be excluded from participation in this study: 1. positive pregnancy test either at screening or just prior to each vaccine administration. 2. female subject who is breastfeeding or plans to breastfeed from the time of the first vaccination through 60 days after the last vaccination. 3. has any medical disease or condition that, in the opinion of the participating site principal investigator (pi) or appropriate sub-investigator, precludes study participation.* *including acute, subacute, intermittent or chronic medical disease or condition that would place the subject at an unacceptable risk of injury, render the subject unable to meet the requirements of the protocol, or may interfere with the evaluation of responses or the subject's successful completion of this trial. 4. presence of self-reported or medically documented significant medical or psychiatric condition(s).* *significant medical or psychiatric conditions include but are not limited to: respiratory disease (e.g., chronic obstructive pulmonary disease [copd], asthma) requiring daily medications currently or any treatment of respiratory disease exacerbations (e.g., asthma exacerbation) in the last 5 years. asthma medications: inhaled, oral, or intravenous (iv) corticosteroids, leukotriene modifiers, long and short acting beta agonists, theophylline, ipratropium, biologics. significant cardiovascular disease (e.g., congestive heart failure, cardiomyopathy, ischemic heart disease), history of myocarditis or pericarditis as an adult, myocardial infarction (mi) within past 6 months, coronary artery bypass surgery or stent placement, or uncontrolled cardiac arrhythmia. neurological or neurodevelopmental conditions (e.g., history of migraines in the past 5 years, epilepsy, stroke, seizures in the last 3 years, encephalopathy, focal neurologic deficits, guillain-barré syndrome, encephalomyelitis, transverse myelitis, stroke or transient ischemic attack, multiple sclerosis, parkinson's disease, amyotrophic lateral sclerosis, creutzfeldt-jakob disease, or alzheimer's disease). ongoing malignancy or recent diagnosis of malignancy in the last five years excluding basal cell and squamous cell carcinoma of the skin, which are allowed. an autoimmune disease, including hypothyroidism without a defined non-autoimmune cause, localized or history of psoriasis. an immunodeficiency of any cause. chronic kidney disease, estimated glomerular filtration rate (egfr) <60 ml/min/1.73m^2. 5. has an acute illness*, as determined by the participating site pi or appropriate sub-investigator, with or without fever [oral temperature >/= 38.0 degrees celsius (100.4 degrees fahrenheit)] within 72 hours prior to each vaccination. *an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the participating site pi or appropriate sub-investigator, the residual symptoms will not interfere with the ability to assess safety parameters as required by the protocol. 6. has a positive test result for hepatitis b surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) types 1 or 2 antibodies at screening. 7. has participated in another investigational study involving any investigational product* within 60 days, or 5 half-lives, whichever is longer, before the first vaccine administration. *study drug, biologic or device 8. currently enrolled in or plans to participate in another clinical trial with an investigational agent* that will be received during the study-reporting period.** *including licensed or unlicensed vaccine, drug, biologic, device, blood product, or medication. **13 months after the first vaccination. 9. has previously participated in an investigational study involving lipid nanoparticles (lnps) (a component of the investigational vaccine assessed in this trial). 10. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to any previous licensed or unlicensed vaccines. 11. chronic use (more than 14 continuous days) of any medications that may be associated with impaired immune responsiveness.* *including, but not limited to, systemic corticosteroids exceeding 10 mg/day of prednisone equivalent, allergy injections, immunoglobulin, interferon, immunomodulators, cytotoxic drugs, or other similar or toxic drugs during the preceding 6-month period prior to vaccine administration (day 1). the use of low dose topical, ophthalmic, inhaled and intranasal steroid preparations will be permitted. 12. anticipating the need for immunosuppressive treatment within the next 6 months. 13. received immunoglobulins and/or any blood or blood products within the 4 months before the first vaccine administration or at any time during the study. 14. has any blood dyscrasias or significant disorder of coagulation. 15. has any chronic liver disease, including fatty liver. 16. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 6 months before the first vaccine administration. 17. has a positive test result for drugs of abuse at screening or before the first vaccine administration. if cannabis is the only detected drug, inclusion is permitted. 18. has any abnormality or permanent body art (e.g., tattoo) that would interfere with the ability to observe local reactions at the injection site (deltoid region). 19. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 20. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 21. receipt of any other sars-cov-2 or other experimental coronavirus vaccine at any time prior to or during the study. 22. close contact of anyone known to have sars-cov-2 infection within 30 days prior to vaccine administration. 23. history of covid-19 diagnosis. 24. on current treatment with investigational agents for prophylaxis of covid-19. 25. current use of any prescription or over-the-counter medications within 7 days prior to vaccination, unless approved by the investigator or necessary to manage a chronic condition. 26. plan to travel outside the united states (us) (continental us, hawaii, and alaska) from enrollment through 28 days after the last vaccination. 27. reside in a nursing home or other skilled nursing facility or have a requirement for skilled nursing care. 28. non-ambulatory. 29. for subjects >/= 56 years of age, history of chronic smoking within the prior year. 30. for subjects >/= 56 years of age, current smoking or vaping. 31. for subjects >/= 56 years of age, individuals currently working with high risk of exposure to sars-cov-2 (e.g., active health care workers with direct patient contact, emergency response personnel). optional substudy

a subject who meets any of the following criteria will be excluded from participation in this study: 1. positive pregnancy test either at screening or just prior to each vaccine administration. 2. female subject who is breastfeeding or plans to breastfeed from the time of the first vaccination through 60 days after the last vaccination. 3. has any medical disease or condition that, in the opinion of the participating site principal investigator (pi) or appropriate sub-investigator, precludes study participation.* *including acute, subacute, intermittent or chronic medical disease or condition that would place the subject at an unacceptable risk of injury, render the subject unable to meet the requirements of the protocol, or may interfere with the evaluation of responses or the subject's successful completion of this trial. 4. presence of self-reported or medically documented significant medical or psychiatric condition(s).* *significant medical or psychiatric conditions include but are not limited to: respiratory disease (e.g., chronic obstructive pulmonary disease [copd], asthma) requiring daily medications currently or any treatment of respiratory disease exacerbations (e.g., asthma exacerbation) in the last 5 years. asthma medications: inhaled, oral, or intravenous (iv) corticosteroids, leukotriene modifiers, long and short acting beta agonists, theophylline, ipratropium, biologics. significant cardiovascular disease (e.g., congestive heart failure, cardiomyopathy, ischemic heart disease), history of myocarditis or pericarditis as an adult, myocardial infarction (mi) within past 6 months, coronary artery bypass surgery or stent placement, or uncontrolled cardiac arrhythmia. neurological or neurodevelopmental conditions (e.g., history of migraines in the past 5 years, epilepsy, stroke, seizures in the last 3 years, encephalopathy, focal neurologic deficits, guillain-barré syndrome, encephalomyelitis, transverse myelitis, stroke or transient ischemic attack, multiple sclerosis, parkinson's disease, amyotrophic lateral sclerosis, creutzfeldt-jakob disease, or alzheimer's disease). ongoing malignancy or recent diagnosis of malignancy in the last five years excluding basal cell and squamous cell carcinoma of the skin, which are allowed. an autoimmune disease, including hypothyroidism without a defined non-autoimmune cause, localized or history of psoriasis. an immunodeficiency of any cause. chronic kidney disease, estimated glomerular filtration rate (egfr) <60 ml/min/1.73m^2. 5. has an acute illness*, as determined by the participating site pi or appropriate sub-investigator, with or without fever [oral temperature >/= 38.0 degrees celsius (100.4 degrees fahrenheit)] within 72 hours prior to each vaccination. *an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the participating site pi or appropriate sub-investigator, the residual symptoms will not interfere with the ability to assess safety parameters as required by the protocol. 6. has a positive test result for hepatitis b surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) types 1 or 2 antibodies at screening. 7. has participated in another investigational study involving any investigational product* within 60 days, or 5 half-lives, whichever is longer, before the first vaccine administration. *study drug, biologic or device 8. currently enrolled in or plans to participate in another clinical trial with an investigational agent* that will be received during the study-reporting period.** *including licensed or unlicensed vaccine, drug, biologic, device, blood product, or medication. **13 months after the first vaccination. 9. has previously participated in an investigational study involving lipid nanoparticles (lnps) (a component of the investigational vaccine assessed in this trial). 10. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to any previous licensed or unlicensed vaccines. 11. chronic use (more than 14 continuous days) of any medications that may be associated with impaired immune responsiveness.* *including, but not limited to, systemic corticosteroids exceeding 10 mg/day of prednisone equivalent, allergy injections, immunoglobulin, interferon, immunomodulators, cytotoxic drugs, or other similar or toxic drugs during the preceding 6-month period prior to vaccine administration (day 1). the use of low dose topical, ophthalmic, inhaled and intranasal steroid preparations will be permitted. 12. anticipating the need for immunosuppressive treatment within the next 6 months. 13. received immunoglobulins and/or any blood or blood products within the 4 months before the first vaccine administration or at any time during the study. 14. has any blood dyscrasias or significant disorder of coagulation. 15. has any chronic liver disease, including fatty liver. 16. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 6 months before the first vaccine administration. 17. has a positive test result for drugs of abuse at screening or before the first vaccine administration. if cannabis is the only detected drug, inclusion is permitted. 18. has any abnormality or permanent body art (e.g., tattoo) that would interfere with the ability to observe local reactions at the injection site (deltoid region). 19. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 20. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 21. receipt of any other sars-cov-2 or other experimental coronavirus vaccine at any time prior to or during the study. 22. close contact of anyone known to have sars-cov-2 infection within 30 days prior to vaccine administration. 23. history of covid-19 diagnosis. 24. on current treatment with investigational agents for prophylaxis of covid-19. 25. current use of any prescription or over-the-counter medications within 7 days prior to vaccination, unless approved by the investigator or necessary to manage a chronic condition. 26. plan to travel outside the united states (us) (continental us, hawaii, and alaska) from enrollment through 28 days after the last vaccination. 27. reside in a nursing home or other skilled nursing facility or have a requirement for skilled nursing care. 28. non-ambulatory. 29. for subjects >/= 56 years of age, history of chronic smoking within the prior year. 30. for subjects >/= 56 years of age, current smoking or vaping. 31. for subjects >/= 56 years of age, individuals currently working with high risk of exposure to sars-cov-2 (e.g., active health care workers with direct patient contact, emergency response personnel). optional substudy

a subject who meets any of the following criteria will be excluded from participation in this study: 1. positive pregnancy test either at screening or just prior to each vaccine administration. 2. female subject who is breastfeeding or plans to breastfeed from the time of the first vaccination through 60 days after the last vaccination. 3. has any medical disease or condition that, in the opinion of the participating site principal investigator (pi) or appropriate sub-investigator, precludes study participation.* *including acute, subacute, intermittent or chronic medical disease or condition that would place the subject at an unacceptable risk of injury, render the subject unable to meet the requirements of the protocol, or may interfere with the evaluation of responses or the subject's successful completion of this trial. 4. presence of self-reported or medically documented significant medical or psychiatric condition(s).* *significant medical or psychiatric conditions include but are not limited to: respiratory disease (e.g., chronic obstructive pulmonary disease [copd], asthma) requiring daily medications currently or any treatment of respiratory disease exacerbations (e.g., asthma exacerbation) in the last 5 years. asthma medications: inhaled, oral, or intravenous (iv) corticosteroids, leukotriene modifiers, long and short acting beta agonists, theophylline, ipratropium, biologics. significant cardiovascular disease (e.g., congestive heart failure, cardiomyopathy, ischemic heart disease), history of myocarditis or pericarditis as an adult, myocardial infarction (mi) within past 6 months, coronary artery bypass surgery or stent placement, or uncontrolled cardiac arrhythmia. neurological or neurodevelopmental conditions (e.g., history of migraines in the past 5 years, epilepsy, stroke, seizures in the last 3 years, encephalopathy, focal neurologic deficits, guillain-barré syndrome, encephalomyelitis, transverse myelitis, stroke or transient ischemic attack, multiple sclerosis, parkinson's disease, amyotrophic lateral sclerosis, creutzfeldt-jakob disease, or alzheimer's disease). ongoing malignancy or recent diagnosis of malignancy in the last five years excluding basal cell and squamous cell carcinoma of the skin, which are allowed. an autoimmune disease, including hypothyroidism without a defined non-autoimmune cause, localized or history of psoriasis. an immunodeficiency of any cause. chronic kidney disease, estimated glomerular filtration rate (egfr) <60 ml/min/1.73m^2. 5. has an acute illness*, as determined by the participating site pi or appropriate sub-investigator, with or without fever [oral temperature >/= 38.0 degrees celsius (100.4 degrees fahrenheit)] within 72 hours prior to each vaccination. *an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the participating site pi or appropriate sub-investigator, the residual symptoms will not interfere with the ability to assess safety parameters as required by the protocol. 6. has a positive test result for hepatitis b surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) types 1 or 2 antibodies at screening. 7. has participated in another investigational study involving any investigational product* within 60 days, or 5 half-lives, whichever is longer, before the first vaccine administration. *study drug, biologic or device 8. currently enrolled in or plans to participate in another clinical trial with an investigational agent* that will be received during the study-reporting period.** *including licensed or unlicensed vaccine, drug, biologic, device, blood product, or medication. **13 months after the first vaccination. 9. has previously participated in an investigational study involving lipid nanoparticles (lnps) (a component of the investigational vaccine assessed in this trial). 10. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to any previous licensed or unlicensed vaccines. 11. chronic use (more than 14 continuous days) of any medications that may be associated with impaired immune responsiveness.* *including, but not limited to, systemic corticosteroids exceeding 10 mg/day of prednisone equivalent, allergy injections, immunoglobulin, interferon, immunomodulators, cytotoxic drugs, or other similar or toxic drugs during the preceding 6-month period prior to vaccine administration (day 1). the use of low dose topical, ophthalmic, inhaled and intranasal steroid preparations will be permitted. 12. anticipating the need for immunosuppressive treatment within the next 6 months. 13. received immunoglobulins and/or any blood or blood products within the 4 months before the first vaccine administration or at any time during the study. 14. has any blood dyscrasias or significant disorder of coagulation. 15. has any chronic liver disease, including fatty liver. 16. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 6 months before the first vaccine administration. 17. has a positive test result for drugs of abuse at screening or before the first vaccine administration. if cannabis is the only detected drug, inclusion is permitted. 18. has any abnormality or permanent body art (e.g., tattoo) that would interfere with the ability to observe local reactions at the injection site (deltoid region). 19. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 20. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 21. receipt of any other sars-cov-2 or other experimental coronavirus vaccine at any time prior to or during the study. 22. close contact of anyone known to have sars-cov-2 infection within 30 days prior to vaccine administration. 23. history of covid-19 diagnosis. 24. on current treatment with investigational agents for prophylaxis of covid-19. 25. current use of any prescription or over-the-counter medications within 7 days prior to vaccination, unless approved by the investigator or necessary to manage a chronic condition. 26. plan to travel outside the united states (us) (continental us, hawaii, and alaska) from enrollment through 28 days after the second vaccination. 27. reside in a nursing home or other skilled nursing facility or have a requirement for skilled nursing care. 28. non-ambulatory. 29. for subjects >/= 56 years of age, history of chronic smoking within the prior year. 30. for subjects >/= 56 years of age, current smoking or vaping. 31. for subjects >/= 56 years of age, individuals currently working with high risk of exposure to sars-cov-2 (e.g., active health care workers with direct patient contact, emergency response personnel).

a subject who meets any of the following criteria will be excluded from participation in this study: 1. positive pregnancy test either at screening or just prior to each vaccine administration. 2. female subject who is breastfeeding or plans to breastfeed from the time of the first vaccination through 60 days after the last vaccination. 3. has any medical disease or condition that, in the opinion of the participating site principal investigator (pi) or appropriate sub-investigator, precludes study participation.* *including acute, subacute, intermittent or chronic medical disease or condition that would place the subject at an unacceptable risk of injury, render the subject unable to meet the requirements of the protocol, or may interfere with the evaluation of responses or the subject's successful completion of this trial. 4. presence of self-reported or medically documented significant medical or psychiatric condition(s).* *significant medical or psychiatric conditions include but are not limited to: respiratory disease (e.g., chronic obstructive pulmonary disease [copd], asthma) requiring daily medications currently or any treatment of respiratory disease exacerbations (e.g., asthma exacerbation) in the last 5 years. asthma medications: inhaled, oral, or intravenous (iv) corticosteroids, leukotriene modifiers, long and short acting beta agonists, theophylline, ipratropium, biologics. significant cardiovascular disease (e.g., congestive heart failure, cardiomyopathy, ischemic heart disease), history of myocarditis or pericarditis as an adult, myocardial infarction (mi) within past 6 months, coronary artery bypass surgery or stent placement, or uncontrolled cardiac arrhythmia. neurological or neurodevelopmental conditions (e.g., history of migraines in the past 5 years, epilepsy, stroke, seizures in the last 3 years, encephalopathy, focal neurologic deficits, guillain-barré syndrome, encephalomyelitis, transverse myelitis, stroke or transient ischemic attack, multiple sclerosis, parkinson's disease, amyotrophic lateral sclerosis, creutzfeldt-jakob disease, or alzheimer's disease). ongoing malignancy or recent diagnosis of malignancy in the last five years excluding basal cell and squamous cell carcinoma of the skin, which are allowed. an autoimmune disease, including hypothyroidism without a defined non-autoimmune cause, localized or history of psoriasis. an immunodeficiency of any cause. chronic kidney disease, estimated glomerular filtration rate (egfr) <60 ml/min/1.73m^2. 5. has an acute illness*, as determined by the participating site pi or appropriate sub-investigator, with or without fever [oral temperature >/= 38.0 degrees celsius (100.4 degrees fahrenheit)] within 72 hours prior to each vaccination. *an acute illness which is nearly resolved with only minor residual symptoms remaining is allowable if, in the opinion of the participating site pi or appropriate sub-investigator, the residual symptoms will not interfere with the ability to assess safety parameters as required by the protocol. 6. has a positive test result for hepatitis b surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) types 1 or 2 antibodies at screening. 7. has participated in another investigational study involving any investigational product* within 60 days, or 5 half-lives, whichever is longer, before the first vaccine administration. *study drug, biologic or device 8. currently enrolled in or plans to participate in another clinical trial with an investigational agent* that will be received during the study-reporting period.** *including licensed or unlicensed vaccine, drug, biologic, device, blood product, or medication. **13 months after the first vaccination. 9. has previously participated in an investigational study involving lipid nanoparticles (lnps) (a component of the investigational vaccine assessed in this trial). 10. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to any previous licensed or unlicensed vaccines. 11. chronic use (more than 14 continuous days) of any medications that may be associated with impaired immune responsiveness.* *including, but not limited to, systemic corticosteroids exceeding 10 mg/day of prednisone equivalent, allergy injections, immunoglobulin, interferon, immunomodulators, cytotoxic drugs, or other similar or toxic drugs during the preceding 6-month period prior to vaccine administration (day 1). the use of low dose topical, ophthalmic, inhaled and intranasal steroid preparations will be permitted. 12. anticipating the need for immunosuppressive treatment within the next 6 months. 13. received immunoglobulins and/or any blood or blood products within the 4 months before the first vaccine administration or at any time during the study. 14. has any blood dyscrasias or significant disorder of coagulation. 15. has any chronic liver disease, including fatty liver. 16. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 6 months before the first vaccine administration. 17. has a positive test result for drugs of abuse at screening or before the first vaccine administration. if cannabis is the only detected drug, inclusion is permitted. 18. has any abnormality or permanent body art (e.g., tattoo) that would interfere with the ability to observe local reactions at the injection site (deltoid region). 19. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 20. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 21. receipt of any other sars-cov-2 or other experimental coronavirus vaccine at any time prior to or during the study. 22. close contact of anyone known to have sars-cov-2 infection within 30 days prior to vaccine administration. 23. history of covid-19 diagnosis. 24. on current treatment with investigational agents for prophylaxis of covid-19. 25. current use of any prescription or over-the-counter medications within 7 days prior to vaccination, unless approved by the investigator or necessary to manage a chronic condition. 26. plan to travel outside the united states (us) (continental us, hawaii, and alaska) from enrollment through 28 days after the second vaccination. 27. reside in a nursing home or other skilled nursing facility or have a requirement for skilled nursing care. 28. non-ambulatory. 29. for subjects >/= 56 years of age, history of chronic smoking within the prior year. 30. for subjects >/= 56 years of age, current smoking or vaping. 31. for subjects >/= 56 years of age, individuals currently working with high risk of exposure to sars-cov-2 (e.g., active health care workers with direct patient contact, emergency response personnel).