participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: 1. pregnant or breastfeeding. 2. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥38.0°celsius/100.4°fahrenheit. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 3. current treatment with investigational agents for prophylaxis against covid-19. 4. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. 5. is a healthcare worker or a member of an emergency response team. 6. current use of any inhaled substance (for example, tobacco or cannabis smoke, nicotine vapors). 7. history of chronic smoking (≥1 cigarette a day) within 1 year of the screening visit (day 0). 8. history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. 9. known history of hypertension, or systolic blood pressure \>150 millimeter of mercury (mmhg) in participants in cohort 1 (≥18 to \<55 years old) or systolic blood pressure \>160 mmhg in participants in cohort 2 (≥55 years old) at the screening visit (day 0). 10. known history of hypotension or systolic blood pressure \<85 mmhg at the screening visit (day 0). 11. diabetes mellitus 12. diagnosis of chronic pulmonary disease (for example, chronic obstructive pulmonary disease, asthma) 13. chronic cardiovascular disease 14. resides in a nursing home 15. grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) 16. current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. 17. received systemic immunosuppressants or immune-modifying drugs for \>14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥20 milligrams (mg)/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). 18. anticipating the need for immunosuppressive treatment at any time during participation in the study. 19. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). 20. history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. 21. bleeding disorder considered a contraindication to im injection or phlebotomy. 22. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). 23. has received or plans to receive a licensed vaccine ≤28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. 24. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. 25. has donated ≥450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. 26. participated in an interventional clinical study (other than mrna-1273 p301) within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. 27. is an immediate family member or household member of study personnel additional key exclusion criteria for part c 1. is sars-cov-2 positive by reverse transcription polymerase chain reaction (rt-pcr) (central or local testing) at baseline or at any time during the mrna-1273-p301 study regardless of the presence or absence of symptoms consistent with covid-19. 2. had any sae in the mrna-1273-p301 study.

participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: 1. pregnant or breastfeeding. 2. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥38.0°celsius/100.4°fahrenheit. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 3. current treatment with investigational agents for prophylaxis against covid-19. 4. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. 5. is a healthcare worker or a member of an emergency response team. 6. current use of any inhaled substance (for example, tobacco or cannabis smoke, nicotine vapors). 7. history of chronic smoking (≥1 cigarette a day) within 1 year of the screening visit (day 0). 8. history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. 9. known history of hypertension, or systolic blood pressure \>150 millimeter of mercury (mmhg) in participants in cohort 1 (≥18 to \<55 years old) or systolic blood pressure \>160 mmhg in participants in cohort 2 (≥55 years old) at the screening visit (day 0). 10. known history of hypotension or systolic blood pressure \<85 mmhg at the screening visit (day 0). 11. diabetes mellitus 12. diagnosis of chronic pulmonary disease (for example, chronic obstructive pulmonary disease, asthma) 13. chronic cardiovascular disease 14. resides in a nursing home 15. grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) 16. current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. 17. received systemic immunosuppressants or immune-modifying drugs for \>14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥20 milligrams (mg)/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). 18. anticipating the need for immunosuppressive treatment at any time during participation in the study. 19. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). 20. history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. 21. bleeding disorder considered a contraindication to im injection or phlebotomy. 22. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). 23. has received or plans to receive a licensed vaccine ≤28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. 24. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. 25. has donated ≥450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. 26. participated in an interventional clinical study (other than mrna-1273 p301) within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. 27. is an immediate family member or household member of study personnel additional key exclusion criteria for part c 1. is sars-cov-2 positive by reverse transcription polymerase chain reaction (rt-pcr) (central or local testing) at baseline or at any time during the mrna-1273-p301 study regardless of the presence or absence of symptoms consistent with covid-19. 2. had any sae in the mrna-1273-p301 study.

participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: pregnant or breastfeeding. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥38.0°celsius/100.4°fahrenheit. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. current treatment with investigational agents for prophylaxis against covid-19. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. is a healthcare worker or a member of an emergency response team. current use of any inhaled substance (for example, tobacco or cannabis smoke, nicotine vapors). history of chronic smoking (≥1 cigarette a day) within 1 year of the screening visit (day 0). history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. known history of hypertension, or systolic blood pressure >150 millimeter of mercury (mmhg) in participants in cohort 1 (≥18 to <55 years old) or systolic blood pressure >160 mmhg in participants in cohort 2 (≥55 years old) at the screening visit (day 0). known history of hypotension or systolic blood pressure <85 mmhg at the screening visit (day 0). diabetes mellitus diagnosis of chronic pulmonary disease (for example, chronic obstructive pulmonary disease, asthma) chronic cardiovascular disease resides in a nursing home grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥20 milligrams (mg)/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). anticipating the need for immunosuppressive treatment at any time during participation in the study. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. bleeding disorder considered a contraindication to im injection or phlebotomy. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). has received or plans to receive a licensed vaccine ≤28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. has donated ≥450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. participated in an interventional clinical study (other than mrna-1273 p301) within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. is an immediate family member or household member of study personnel additional key exclusion criteria for part c is sars-cov-2 positive by reverse transcription polymerase chain reaction (rt-pcr) (central or local testing) at baseline or at any time during the mrna-1273-p301 study regardless of the presence or absence of symptoms consistent with covid-19. had any sae in the mrna-1273-p301 study.

participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: pregnant or breastfeeding. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥38.0°celsius/100.4°fahrenheit. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. current treatment with investigational agents for prophylaxis against covid-19. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. is a healthcare worker or a member of an emergency response team. current use of any inhaled substance (for example, tobacco or cannabis smoke, nicotine vapors). history of chronic smoking (≥1 cigarette a day) within 1 year of the screening visit (day 0). history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. known history of hypertension, or systolic blood pressure >150 millimeter of mercury (mmhg) in participants in cohort 1 (≥18 to <55 years old) or systolic blood pressure >160 mmhg in participants in cohort 2 (≥55 years old) at the screening visit (day 0). known history of hypotension or systolic blood pressure <85 mmhg at the screening visit (day 0). diabetes mellitus diagnosis of chronic pulmonary disease (for example, chronic obstructive pulmonary disease, asthma) chronic cardiovascular disease resides in a nursing home grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥20 milligrams (mg)/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). anticipating the need for immunosuppressive treatment at any time during participation in the study. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. bleeding disorder considered a contraindication to im injection or phlebotomy. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). has received or plans to receive a licensed vaccine ≤28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. has donated ≥450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. participated in an interventional clinical study (other than mrna-1273 p301) within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. is an immediate family member or household member of study personnel additional key exclusion criteria for part c is sars-cov-2 positive by reverse transcription polymerase chain reaction (rt-pcr) (central or local testing) at baseline or at any time during the mrna-1273-p301 study regardless of the presence or absence of symptoms consistent with covid-19. had any sae in the mrna-1273-p301 study.

participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: 1. pregnant or breastfeeding. 2. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥38.0°celsius/100.4°fahrenheit. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 3. current treatment with investigational agents for prophylaxis against covid-19. 4. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. 5. is a healthcare worker or a member of an emergency response team. 6. current use of any inhaled substance (for example, tobacco or cannabis smoke, nicotine vapors). 7. history of chronic smoking (≥1 cigarette a day) within 1 year of the screening visit (day 0). 8. history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. 9. known history of hypertension, or systolic blood pressure >150 millimeter of mercury (mmhg) in participants in cohort 1 (≥18 to <55 years old) or systolic blood pressure >160 mmhg in participants in cohort 2 (≥55 years old) at the screening visit (day 0). 10. known history of hypotension or systolic blood pressure <85 mmhg at the screening visit (day 0). 11. diabetes mellitus 12. diagnosis of chronic pulmonary disease (for example, chronic obstructive pulmonary disease, asthma) 13. chronic cardiovascular disease 14. resides in a nursing home 15. grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) 16. current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. 17. received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥20 milligrams (mg)/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). 18. anticipating the need for immunosuppressive treatment at any time during participation in the study. 19. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). 20. history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. 21. bleeding disorder considered a contraindication to im injection or phlebotomy. 22. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). 23. has received or plans to receive a licensed vaccine ≤28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. 24. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. 25. has donated ≥450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. 26. participated in an interventional clinical study (other than mrna-1273 p301) within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. 27. is an immediate family member or household member of study personnel additional key exclusion criteria for part c 1. is sars-cov-2 positive by reverse transcription polymerase chain reaction (rt-pcr) (central or local testing) at baseline or at any time during the mrna-1273-p301 study regardless of the presence or absence of symptoms consistent with covid-19. 2. had any sae in the mrna-1273-p301 study.

participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: 1. pregnant or breastfeeding. 2. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥38.0°celsius/100.4°fahrenheit. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 3. current treatment with investigational agents for prophylaxis against covid-19. 4. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. 5. is a healthcare worker or a member of an emergency response team. 6. current use of any inhaled substance (for example, tobacco or cannabis smoke, nicotine vapors). 7. history of chronic smoking (≥1 cigarette a day) within 1 year of the screening visit (day 0). 8. history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. 9. known history of hypertension, or systolic blood pressure >150 millimeter of mercury (mmhg) in participants in cohort 1 (≥18 to <55 years old) or systolic blood pressure >160 mmhg in participants in cohort 2 (≥55 years old) at the screening visit (day 0). 10. known history of hypotension or systolic blood pressure <85 mmhg at the screening visit (day 0). 11. diabetes mellitus 12. diagnosis of chronic pulmonary disease (for example, chronic obstructive pulmonary disease, asthma) 13. chronic cardiovascular disease 14. resides in a nursing home 15. grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) 16. current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. 17. received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥20 milligrams (mg)/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). 18. anticipating the need for immunosuppressive treatment at any time during participation in the study. 19. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). 20. history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. 21. bleeding disorder considered a contraindication to im injection or phlebotomy. 22. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). 23. has received or plans to receive a licensed vaccine ≤28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. 24. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. 25. has donated ≥450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. 26. participated in an interventional clinical study (other than mrna-1273 p301) within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. 27. is an immediate family member or household member of study personnel additional key exclusion criteria for part c 1. is sars-cov-2 positive by reverse transcription polymerase chain reaction (rt-pcr) (central or local testing) at baseline or at any time during the mrna-1273-p301 study regardless of the presence or absence of symptoms consistent with covid-19. 2. had any sae in the mrna-1273-p301 study.

participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: 1. pregnant or breastfeeding. 2. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥38.0°celsius/100.4°fahrenheit. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 3. current treatment with investigational agents for prophylaxis against covid-19. 4. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. 5. is a healthcare worker or a member of an emergency response team. 6. current use of any inhaled substance (for example, tobacco or cannabis smoke, nicotine vapors). 7. history of chronic smoking (≥1 cigarette a day) within 1 year of the screening visit (day 0). 8. history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. 9. known history of hypertension, or systolic blood pressure >150 millimeter of mercury (mmhg) in participants in cohort 1 (≥18 to <55 years old) or systolic blood pressure >160 mmhg in participants in cohort 2 (≥55 years old) at the screening visit (day 0). 10. known history of hypotension or systolic blood pressure <85 mmhg at the screening visit (day 0). 11. diabetes mellitus 12. diagnosis of chronic pulmonary disease (for example, chronic obstructive pulmonary disease, asthma) 13. chronic cardiovascular disease 14. resides in a nursing home 15. grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) 16. current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. 17. received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥20 milligrams (mg)/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). 18. anticipating the need for immunosuppressive treatment at any time during participation in the study. 19. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). 20. history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. 21. bleeding disorder considered a contraindication to im injection or phlebotomy. 22. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). 23. has received or plans to receive a licensed vaccine ≤28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. 24. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. 25. has donated ≥450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. 26. participated in an interventional clinical study within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. 27. is an immediate family member or household member of study personnel

participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: 1. pregnant or breastfeeding. 2. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥38.0°celsius/100.4°fahrenheit. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 3. current treatment with investigational agents for prophylaxis against covid-19. 4. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. 5. is a healthcare worker or a member of an emergency response team. 6. current use of any inhaled substance (for example, tobacco or cannabis smoke, nicotine vapors). 7. history of chronic smoking (≥1 cigarette a day) within 1 year of the screening visit (day 0). 8. history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. 9. known history of hypertension, or systolic blood pressure >150 millimeter of mercury (mmhg) in participants in cohort 1 (≥18 to <55 years old) or systolic blood pressure >160 mmhg in participants in cohort 2 (≥55 years old) at the screening visit (day 0). 10. known history of hypotension or systolic blood pressure <85 mmhg at the screening visit (day 0). 11. diabetes mellitus 12. diagnosis of chronic pulmonary disease (for example, chronic obstructive pulmonary disease, asthma) 13. chronic cardiovascular disease 14. resides in a nursing home 15. grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) 16. current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. 17. received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥20 milligrams (mg)/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). 18. anticipating the need for immunosuppressive treatment at any time during participation in the study. 19. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). 20. history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. 21. bleeding disorder considered a contraindication to im injection or phlebotomy. 22. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). 23. has received or plans to receive a licensed vaccine ≤28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. 24. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. 25. has donated ≥450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. 26. participated in an interventional clinical study within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. 27. is an immediate family member or household member of study personnel

participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: 1. known history of sars-cov-2 infection or known exposure to someone with sars cov 2 infection or covid-19. 2. travel outside of the us in the 28 days prior to the screening visit (day 0). 3. pregnant or breastfeeding. 4. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥38.0°celsius/100.4°fahrenheit. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 5. prior administration of an investigational cov (for example, sars-cov-2, sars-cov, mers-cov) vaccine. 6. current treatment with investigational agents for prophylaxis against covid-19. 7. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. 8. is a healthcare worker or a member of an emergency response team. 9. current use of any inhaled substance (for example, tobacco or cannabis smoke, nicotine vapors). 10. history of chronic smoking (≥1 cigarette a day) within 1 year of the screening visit (day 0). 11. history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. 12. known history of hypertension, or systolic blood pressure >150 millimeter of mercury (mmhg) in participants in cohort 1 (≥18 to <55 years old) or systolic blood pressure >160 mmhg in participants in cohort 2 (≥55 years old) at the screening visit (day 0). 13. known history of hypotension or systolic blood pressure <85 mmhg at the screening visit (day 0). 14. diabetes mellitus 15. diagnosis of chronic pulmonary disease (for example, chronic obstructive pulmonary disease, asthma) 16. chronic cardiovascular disease 17. resides in a nursing home 18. grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) 19. current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. 20. received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥20 mg/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). 21. anticipating the need for immunosuppressive treatment at any time during participation in the study. 22. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). 23. history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. 24. bleeding disorder considered a contraindication to im injection or phlebotomy. 25. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). 26. has received or plans to receive a licensed vaccine ≤28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. 27. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. 28. has donated ≥450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. 29. participated in an interventional clinical study within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. 30. is an immediate family member or household member of study personnel

participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: 1. known history of sars-cov-2 infection or known exposure to someone with sars cov 2 infection or covid-19. 2. travel outside of the us in the 28 days prior to the screening visit (day 0). 3. pregnant or breastfeeding. 4. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥38.0°celsius/100.4°fahrenheit. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 5. prior administration of an investigational cov (for example, sars-cov-2, sars-cov, mers-cov) vaccine. 6. current treatment with investigational agents for prophylaxis against covid-19. 7. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. 8. is a healthcare worker or a member of an emergency response team. 9. current use of any inhaled substance (for example, tobacco or cannabis smoke, nicotine vapors). 10. history of chronic smoking (≥1 cigarette a day) within 1 year of the screening visit (day 0). 11. history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. 12. known history of hypertension, or systolic blood pressure >150 millimeter of mercury (mmhg) in participants in cohort 1 (≥18 to <55 years old) or systolic blood pressure >160 mmhg in participants in cohort 2 (≥55 years old) at the screening visit (day 0). 13. known history of hypotension or systolic blood pressure <85 mmhg at the screening visit (day 0). 14. diabetes mellitus 15. diagnosis of chronic pulmonary disease (for example, chronic obstructive pulmonary disease, asthma) 16. chronic cardiovascular disease 17. resides in a nursing home 18. grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) 19. current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. 20. received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥20 mg/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). 21. anticipating the need for immunosuppressive treatment at any time during participation in the study. 22. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). 23. history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. 24. bleeding disorder considered a contraindication to im injection or phlebotomy. 25. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). 26. has received or plans to receive a licensed vaccine ≤28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. 27. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. 28. has donated ≥450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. 29. participated in an interventional clinical study within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. 30. is an immediate family member or household member of study personnel

participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: 1. known history of sars-cov-2 infection or known exposure to someone with sars cov 2 infection or covid-19. 2. travel outside of the us in the 28 days prior to the screening visit (day 0). 3. pregnant or breastfeeding. 4. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥ 38.0°c/100.4°f. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 5. prior administration of an investigational cov (eg, sars-cov-2, sars-cov, mers-cov) vaccine. 6. current treatment with investigational agents for prophylaxis against covid-19. 7. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. 8. is a healthcare worker or a member of an emergency response team. 9. current use of any inhaled substance (eg, tobacco or cannabis smoke, nicotine vapors). 10. history of chronic smoking (≥ 1 cigarette a day) within 1 year of the screening visit (day 0). 11. history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. 12. known history of hypertension, or systolic blood pressure > 150 mm hg in participants in cohort 1 (≥ 18 to < 55 years old) or systolic blood pressure > 160 mm hg in participants in cohort 2 (≥ 55 years old) at the screening visit (day 0).. 13. known history of hypotension or systolic blood pressure < 85 mm hg at the screening visit (day 0). 14. diabetes mellitus 15. diagnosis of chronic pulmonary disease (eg, chronic obstructive pulmonary disease, asthma) 16. chronic cardiovascular disease 17. resides in a nursing home 18. grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) 19. current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. 20. received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥ 20 mg/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). 21. anticipating the need for immunosuppressive treatment at any time during participation in the study. 22. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). 23. history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. 24. bleeding disorder considered a contraindication to im injection or phlebotomy. 25. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). 26. has received or plans to receive a licensed vaccine ≤ 28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. 27. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. 28. has donated ≥ 450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. 29. participated in an interventional clinical study within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. 30. is an immediate family member or household member of study personnel

participants meeting any of the following criteria at the screening visit (day 0) or at day 1, unless noted otherwise, will be excluded from the study: 1. known history of sars-cov-2 infection or known exposure to someone with sars cov 2 infection or covid-19. 2. travel outside of the us in the 28 days prior to the screening visit (day 0). 3. pregnant or breastfeeding. 4. is acutely ill or febrile 24 hours prior to or at the screening visit (day 0). fever is defined as a body temperature ≥ 38.0°c/100.4°f. participants meeting this criterion may be rescheduled within the relevant window periods. afebrile participants with minor illnesses can be enrolled at the discretion of the investigator. 5. prior administration of an investigational cov (eg, sars-cov-2, sars-cov, mers-cov) vaccine. 6. current treatment with investigational agents for prophylaxis against covid-19. 7. has a medical, psychiatric, or occupational condition that may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the investigator's judgment. 8. is a healthcare worker or a member of an emergency response team. 9. current use of any inhaled substance (eg, tobacco or cannabis smoke, nicotine vapors). 10. history of chronic smoking (≥ 1 cigarette a day) within 1 year of the screening visit (day 0). 11. history of illegal substance use or alcohol abuse within the past 2 years. this exclusion does not apply to historical cannabis use that was formerly illegal in the participant's state but is legal at the time of screening. 12. known history of hypertension, or systolic blood pressure > 150 mm hg in participants in cohort 1 (≥ 18 to < 55 years old) or systolic blood pressure > 160 mm hg in participants in cohort 2 (≥ 55 years old) at the screening visit (day 0).. 13. known history of hypotension or systolic blood pressure < 85 mm hg at the screening visit (day 0). 14. diabetes mellitus 15. diagnosis of chronic pulmonary disease (eg, chronic obstructive pulmonary disease, asthma) 16. chronic cardiovascular disease 17. resides in a nursing home 18. grade 1 or higher toxicity on clinical safety laboratory testing at the screening visit (day 0) 19. current or previous diagnosis of immunocompromising condition, immune-mediated disease, or other immunosuppressive condition. 20. received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 6 months prior to the screening visit (day 0) (for corticosteroids ≥ 20 mg/day of prednisone equivalent). topical tacrolimus is allowed if not used within 14 days prior to the screening visit (day 0). 21. anticipating the need for immunosuppressive treatment at any time during participation in the study. 22. positive serology for hepatitis b virus surface antigen, hepatitis c virus antibody, or human immunodeficiency virus (hiv) type 1 or 2 antibodies identified at the screening visit (day 0). 23. history of anaphylaxis, urticaria, or other significant ar requiring medical intervention after receipt of a vaccine. 24. bleeding disorder considered a contraindication to im injection or phlebotomy. 25. diagnosis of malignancy within previous 10 years (excluding non-melanoma skin cancer). 26. has received or plans to receive a licensed vaccine ≤ 28 days prior to the first injection (day 1) or plans to receive a licensed vaccine within 28 days before or after any study injection. licensed influenza vaccines may be received more than 14 days before or after any study injection. 27. receipt of systemic immunoglobulins or blood products within 3 months prior to the screening visit (day 0) or plans for receipt during the study. 28. has donated ≥ 450 ml of blood products within 28 days prior to the screening visit (day 0) or plans to donate blood products during the study. 29. participated in an interventional clinical study within 28 days prior to the screening visit (day 0) or plans to do so while participating in this study. 30. is an immediate family member or household member of study personnel