1. positive pregnancy test prior to each vaccine administration. 2. bmi \> 40.0 kg / m\^2. 3. female subject who is breastfeeding. 4. has any medical disease or condition that, in the opinion of the participating site 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. 5. 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. type 2 diabetes mellitus, not including prediabetes. 6. 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. 7. has participated in another investigational study involving any investigational product\* within 5 half-lives 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. \*\* up to 15 months after the first vaccination. 9. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to drugs or any previous licensed or unlicensed vaccines or to polyethylene glycol (peg) or a peg-containing product. 10. 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. 11. anticipating the need for immunosuppressive treatment within the next 6 months. 12. 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. 13. has any blood dyscrasias or significant disorder of coagulation. 14. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 15. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 16. receipt of any other sars-cov-2 vaccine or any experimental coronavirus vaccine at any time prior to or during the study, except cohort 1 subjects who received mrna-1273 in dmid 20-0003. 17. close contact of anyone known to have sars-cov-2 infection within 14 days prior to vaccine administration. 18. history of covid-19 diagnosis, positive sars-cov-2 pcr test, or, for cohort 2 only, a known positive sars-cov-2 serologic test. 19. on current treatment with investigational agents for prophylaxis of covid-19.

1. positive pregnancy test prior to each vaccine administration. 2. bmi \> 40.0 kg / m\^2. 3. female subject who is breastfeeding. 4. has any medical disease or condition that, in the opinion of the participating site 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. 5. 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. type 2 diabetes mellitus, not including prediabetes. 6. 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. 7. has participated in another investigational study involving any investigational product\* within 5 half-lives 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. \*\* up to 15 months after the first vaccination. 9. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to drugs or any previous licensed or unlicensed vaccines or to polyethylene glycol (peg) or a peg-containing product. 10. 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. 11. anticipating the need for immunosuppressive treatment within the next 6 months. 12. 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. 13. has any blood dyscrasias or significant disorder of coagulation. 14. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 15. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 16. receipt of any other sars-cov-2 vaccine or any experimental coronavirus vaccine at any time prior to or during the study, except cohort 1 subjects who received mrna-1273 in dmid 20-0003. 17. close contact of anyone known to have sars-cov-2 infection within 14 days prior to vaccine administration. 18. history of covid-19 diagnosis, positive sars-cov-2 pcr test, or, for cohort 2 only, a known positive sars-cov-2 serologic test. 19. on current treatment with investigational agents for prophylaxis of covid-19.

positive pregnancy test prior to each vaccine administration. bmi > 40.0 kg / m^2. female subject who is breastfeeding. has any medical disease or condition that, in the opinion of the participating site 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. type 2 diabetes mellitus, not including prediabetes. 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 participated in another investigational study involving any investigational product* within 5 half-lives 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. ** up to 15 months after the first vaccination. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to drugs or any previous licensed or unlicensed vaccines or to polyethylene glycol (peg) or a peg-containing product. 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. 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 vaccine or any experimental coronavirus vaccine at any time prior to or during the study, except cohort 1 subjects who received mrna-1273 in dmid 20-0003. close contact of anyone known to have sars-cov-2 infection within 14 days prior to vaccine administration. history of covid-19 diagnosis, positive sars-cov-2 pcr test, or, for cohort 2 only, a known positive sars-cov-2 serologic test. on current treatment with investigational agents for prophylaxis of covid-19.

positive pregnancy test prior to each vaccine administration. bmi > 40.0 kg / m^2. female subject who is breastfeeding. has any medical disease or condition that, in the opinion of the participating site 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. type 2 diabetes mellitus, not including prediabetes. 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 participated in another investigational study involving any investigational product* within 5 half-lives 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. ** up to 15 months after the first vaccination. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to drugs or any previous licensed or unlicensed vaccines or to polyethylene glycol (peg) or a peg-containing product. 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. 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 vaccine or any experimental coronavirus vaccine at any time prior to or during the study, except cohort 1 subjects who received mrna-1273 in dmid 20-0003. close contact of anyone known to have sars-cov-2 infection within 14 days prior to vaccine administration. history of covid-19 diagnosis, positive sars-cov-2 pcr test, or, for cohort 2 only, a known positive sars-cov-2 serologic test. on current treatment with investigational agents for prophylaxis of covid-19.

1. positive pregnancy test prior to each vaccine administration. 2. bmi > 40.0 kg / m^2. 3. female subject who is breastfeeding. 4. has any medical disease or condition that, in the opinion of the participating site 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. 5. 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. type 2 diabetes mellitus, not including prediabetes. 6. 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. 7. has participated in another investigational study involving any investigational product* within 5 half-lives 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. ** up to 15 months after the first vaccination. 9. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to drugs or any previous licensed or unlicensed vaccines or to polyethylene glycol (peg) or a peg-containing product. 10. 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. 11. anticipating the need for immunosuppressive treatment within the next 6 months. 12. 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. 13. has any blood dyscrasias or significant disorder of coagulation. 14. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 15. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 16. receipt of any other sars-cov-2 vaccine or any experimental coronavirus vaccine at any time prior to or during the study, except cohort 1 subjects who received mrna-1273 in dmid 20-0003. 17. close contact of anyone known to have sars-cov-2 infection within 14 days prior to vaccine administration. 18. history of covid-19 diagnosis, positive sars-cov-2 pcr test, or, for cohort 2 only, a known positive sars-cov-2 serologic test. 19. on current treatment with investigational agents for prophylaxis of covid-19.

1. positive pregnancy test prior to each vaccine administration. 2. bmi > 40.0 kg / m^2. 3. female subject who is breastfeeding. 4. has any medical disease or condition that, in the opinion of the participating site 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. 5. 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. type 2 diabetes mellitus, not including prediabetes. 6. 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. 7. has participated in another investigational study involving any investigational product* within 5 half-lives 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. ** up to 15 months after the first vaccination. 9. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to drugs or any previous licensed or unlicensed vaccines or to polyethylene glycol (peg) or a peg-containing product. 10. 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. 11. anticipating the need for immunosuppressive treatment within the next 6 months. 12. 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. 13. has any blood dyscrasias or significant disorder of coagulation. 14. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 15. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 16. receipt of any other sars-cov-2 vaccine or any experimental coronavirus vaccine at any time prior to or during the study, except cohort 1 subjects who received mrna-1273 in dmid 20-0003. 17. close contact of anyone known to have sars-cov-2 infection within 14 days prior to vaccine administration. 18. history of covid-19 diagnosis, positive sars-cov-2 pcr test, or, for cohort 2 only, a known positive sars-cov-2 serologic test. 19. on current treatment with investigational agents for prophylaxis of covid-19.

positive pregnancy test prior to each vaccine administration. bmi > 40.0 kg / m^2. female subject who is breastfeeding. has any medical disease or condition that, in the opinion of the participating site 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. type 2 diabetes mellitus, not including prediabetes. 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 participated in another investigational study involving any investigational product* within 5 half-lives 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. ** up to 15 months after the first vaccination. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to drugs or any previous licensed or unlicensed vaccines or to polyethylene glycol (peg) or a peg-containing product. 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. 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 vaccine or any experimental coronavirus vaccine at any time prior to or during the study, except cohort 1 subjects who received mrna-1273 in dmid 20-0003. close contact of anyone known to have sars-cov-2 infection within 14 days prior to vaccine administration. history of covid-19 diagnosis, positive sars-cov-2 pcr test, or, for cohort 2 only, a known positive sars-cov-2 serologic test. on current treatment with investigational agents for prophylaxis of covid-19.

positive pregnancy test prior to each vaccine administration. bmi > 40.0 kg / m^2. female subject who is breastfeeding. has any medical disease or condition that, in the opinion of the participating site 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. type 2 diabetes mellitus, not including prediabetes. 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 participated in another investigational study involving any investigational product* within 5 half-lives 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. ** up to 15 months after the first vaccination. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to drugs or any previous licensed or unlicensed vaccines or to polyethylene glycol (peg) or a peg-containing product. 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. 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 vaccine or any experimental coronavirus vaccine at any time prior to or during the study, except cohort 1 subjects who received mrna-1273 in dmid 20-0003. close contact of anyone known to have sars-cov-2 infection within 14 days prior to vaccine administration. history of covid-19 diagnosis, positive sars-cov-2 pcr test, or, for cohort 2 only, a known positive sars-cov-2 serologic test. on current treatment with investigational agents for prophylaxis of covid-19.

1. positive pregnancy test prior to each vaccine administration. 2. bmi > 40.0 kg / m^2. 3. female subject who is breastfeeding. 4. has any medical disease or condition that, in the opinion of the participating site 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. 5. 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. type 2 diabetes mellitus, not including prediabetes. 6. 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. 7. has participated in another investigational study involving any investigational product* within 5 half-lives 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. ** up to 15 months after the first vaccination. 9. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to drugs or any previous licensed or unlicensed vaccines or to polyethylene glycol (peg) or a peg-containing product. 10. 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. 11. anticipating the need for immunosuppressive treatment within the next 6 months. 12. 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. 13. has any blood dyscrasias or significant disorder of coagulation. 14. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 15. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 16. receipt of any other sars-cov-2 vaccine or any experimental coronavirus vaccine at any time prior to or during the study, except cohort 1 subjects who received mrna-1273 in dmid 20-0003. 17. close contact of anyone known to have sars-cov-2 infection within 14 days prior to vaccine administration. 18. history of covid-19 diagnosis, positive sars-cov-2 pcr test, or, for cohort 2 only, a known positive sars-cov-2 serologic test. 19. on current treatment with investigational agents for prophylaxis of covid-19.

1. positive pregnancy test prior to each vaccine administration. 2. bmi > 40.0 kg / m^2. 3. female subject who is breastfeeding. 4. has any medical disease or condition that, in the opinion of the participating site 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. 5. 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. type 2 diabetes mellitus, not including prediabetes. 6. 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. 7. has participated in another investigational study involving any investigational product* within 5 half-lives 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. ** up to 15 months after the first vaccination. 9. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to drugs or any previous licensed or unlicensed vaccines or to polyethylene glycol (peg) or a peg-containing product. 10. 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. 11. anticipating the need for immunosuppressive treatment within the next 6 months. 12. 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. 13. has any blood dyscrasias or significant disorder of coagulation. 14. received or plans to receive a licensed, live vaccine within 4 weeks before or after each vaccination. 15. received or plans to receive a licensed, inactivated vaccine within 2 weeks before or after each vaccination. 16. receipt of any other sars-cov-2 vaccine or any experimental coronavirus vaccine at any time prior to or during the study, except cohort 1 subjects who received mrna-1273 in dmid 20-0003. 17. close contact of anyone known to have sars-cov-2 infection within 14 days prior to vaccine administration. 18. history of covid-19 diagnosis, positive sars-cov-2 pcr test, or, for cohort 2 only, a known positive sars-cov-2 serologic test. 19. on current treatment with investigational agents for prophylaxis of covid-19.