1. positive urine pregnancy test at screening. 2. any medical disease or condition that, in the opinion of the site principal investigator (pi) or appropriate sub-investigator, precludes study participation. 3. presence of self-reported or medically documented uncontrolled significant medical or psychiatric condition(s) other than covid-19. 4. reports a recent positive test result (within the past 6 months) for hepatitis b surface antigen, hepatitis c virus antibody, or hiv-1 antibodies at screening. 5. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 1 month of study day 1. 6. covid-19 signs associated with acute respiratory distress or imminent serious medical outcomes. \^\^ 7. bmi ≥36 8. subjects living (e.g., siblings, spouses, relatives, roommates) in the same household cannot be enrolled. 9. has participated in another investigational study involving any intervention for sars-cov-2/covid- 19 within the past 6 months or any clinical trial with interventional investigational product within 30 days of screening. 10. currently enrolled in or plans to participate in another clinical trial with an interventional investigational agent that will be received during the studyperiod. 11. history of hospitalization within the past 60 days. 12. history of systemic antiviral therapies within the past 30 days. 13. history of oral corticoid steroid use within the past 14 days or steroid injection within the past 6 months. active use of nasal or inhalable steroids is also exclusionary. topical steroids are not exclusionary. 14. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to nitrites, nitrates, or sun exposure. 15. has any oral abnormality (e.g. ulcer, oral mucositis, gingivitis) that in the opinion of the investigator would interfere with device use, or intra-oral metal body piercings that cannot be removed for the duration of the study. metal orthodontia is permitted as braces will be covered by the device mouthpiece.

1. positive urine pregnancy test at screening. 2. any medical disease or condition that, in the opinion of the site principal investigator (pi) or appropriate sub-investigator, precludes study participation. 3. presence of self-reported or medically documented uncontrolled significant medical or psychiatric condition(s) other than covid-19. 4. reports a recent positive test result (within the past 6 months) for hepatitis b surface antigen, hepatitis c virus antibody, or hiv-1 antibodies at screening. 5. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 1 month of study day 1. 6. covid-19 signs associated with acute respiratory distress or imminent serious medical outcomes. \^\^ 7. bmi ≥36 8. subjects living (e.g., siblings, spouses, relatives, roommates) in the same household cannot be enrolled. 9. has participated in another investigational study involving any intervention for sars-cov-2/covid- 19 within the past 6 months or any clinical trial with interventional investigational product within 30 days of screening. 10. currently enrolled in or plans to participate in another clinical trial with an interventional investigational agent that will be received during the studyperiod. 11. history of hospitalization within the past 60 days. 12. history of systemic antiviral therapies within the past 30 days. 13. history of oral corticoid steroid use within the past 14 days or steroid injection within the past 6 months. active use of nasal or inhalable steroids is also exclusionary. topical steroids are not exclusionary. 14. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to nitrites, nitrates, or sun exposure. 15. has any oral abnormality (e.g. ulcer, oral mucositis, gingivitis) that in the opinion of the investigator would interfere with device use, or intra-oral metal body piercings that cannot be removed for the duration of the study. metal orthodontia is permitted as braces will be covered by the device mouthpiece.

positive urine pregnancy test at screening. any medical disease or condition that, in the opinion of the site principal investigator (pi) or appropriate sub-investigator, precludes study participation. presence of self-reported or medically documented uncontrolled significant medical or psychiatric condition(s) other than covid-19. reports a recent positive test result (within the past 6 months) for hepatitis b surface antigen, hepatitis c virus antibody, or hiv-1 antibodies at screening. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 1 month of study day 1. covid-19 signs associated with acute respiratory distress or imminent serious medical outcomes. ^^ bmi ≥36 subjects living (e.g., siblings, spouses, relatives, roommates) in the same household cannot be enrolled. has participated in another investigational study involving any intervention for sars-cov-2/covid- 19 within the past 6 months or any clinical trial with interventional investigational product within 30 days of screening. currently enrolled in or plans to participate in another clinical trial with an interventional investigational agent that will be received during the studyperiod. history of hospitalization within the past 60 days. history of systemic antiviral therapies within the past 30 days. history of oral corticoid steroid use within the past 14 days or steroid injection within the past 6 months. active use of nasal or inhalable steroids is also exclusionary. topical steroids are not exclusionary. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to nitrites, nitrates, or sun exposure. has any oral abnormality (e.g. ulcer, oral mucositis, gingivitis) that in the opinion of the investigator would interfere with device use, or intra-oral metal body piercings that cannot be removed for the duration of the study. metal orthodontia is permitted as braces will be covered by the device mouthpiece.

positive urine pregnancy test at screening. any medical disease or condition that, in the opinion of the site principal investigator (pi) or appropriate sub-investigator, precludes study participation. presence of self-reported or medically documented uncontrolled significant medical or psychiatric condition(s) other than covid-19. reports a recent positive test result (within the past 6 months) for hepatitis b surface antigen, hepatitis c virus antibody, or hiv-1 antibodies at screening. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 1 month of study day 1. covid-19 signs associated with acute respiratory distress or imminent serious medical outcomes. ^^ bmi ≥36 subjects living (e.g., siblings, spouses, relatives, roommates) in the same household cannot be enrolled. has participated in another investigational study involving any intervention for sars-cov-2/covid- 19 within the past 6 months or any clinical trial with interventional investigational product within 30 days of screening. currently enrolled in or plans to participate in another clinical trial with an interventional investigational agent that will be received during the studyperiod. history of hospitalization within the past 60 days. history of systemic antiviral therapies within the past 30 days. history of oral corticoid steroid use within the past 14 days or steroid injection within the past 6 months. active use of nasal or inhalable steroids is also exclusionary. topical steroids are not exclusionary. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to nitrites, nitrates, or sun exposure. has any oral abnormality (e.g. ulcer, oral mucositis, gingivitis) that in the opinion of the investigator would interfere with device use, or intra-oral metal body piercings that cannot be removed for the duration of the study. metal orthodontia is permitted as braces will be covered by the device mouthpiece.

1. positive urine pregnancy test at screening. 2. any medical disease or condition that, in the opinion of the site principal investigator (pi) or appropriate sub-investigator, precludes study participation. 3. presence of self-reported or medically documented uncontrolled significant medical or psychiatric condition(s) other than covid-19. 4. reports a recent positive test result (within the past 6 months) for hepatitis b surface antigen, hepatitis c virus antibody, or hiv-1 antibodies at screening. 5. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 1 month of study day 1. 6. covid-19 signs associated with acute respiratory distress or imminent serious medical outcomes. ^^ 7. bmi ≥36 8. subjects living (e.g., siblings, spouses, relatives, roommates) in the same household cannot be enrolled. 9. has participated in another investigational study involving any intervention for sars-cov-2/covid- 19 within the past 6 months or any clinical trial with interventional investigational product within 30 days of screening. 10. currently enrolled in or plans to participate in another clinical trial with an interventional investigational agent that will be received during the studyperiod. 11. history of hospitalization within the past 60 days. 12. history of systemic antiviral therapies within the past 30 days. 13. history of oral corticoid steroid use within the past 14 days or steroid injection within the past 6 months. active use of nasal or inhalable steroids is also exclusionary. topical steroids are not exclusionary. 14. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to nitrites, nitrates, or sun exposure. 15. has any oral abnormality (e.g. ulcer, oral mucositis, gingivitis) that in the opinion of the investigator would interfere with device use, or intra-oral metal body piercings that cannot be removed for the duration of the study. metal orthodontia is permitted as braces will be covered by the device mouthpiece.

1. positive urine pregnancy test at screening. 2. any medical disease or condition that, in the opinion of the site principal investigator (pi) or appropriate sub-investigator, precludes study participation. 3. presence of self-reported or medically documented uncontrolled significant medical or psychiatric condition(s) other than covid-19. 4. reports a recent positive test result (within the past 6 months) for hepatitis b surface antigen, hepatitis c virus antibody, or hiv-1 antibodies at screening. 5. has a history of alcohol abuse or other recreational drug (excluding cannabis) use within 1 month of study day 1. 6. covid-19 signs associated with acute respiratory distress or imminent serious medical outcomes. ^^ 7. bmi ≥36 8. subjects living (e.g., siblings, spouses, relatives, roommates) in the same household cannot be enrolled. 9. has participated in another investigational study involving any intervention for sars-cov-2/covid- 19 within the past 6 months or any clinical trial with interventional investigational product within 30 days of screening. 10. currently enrolled in or plans to participate in another clinical trial with an interventional investigational agent that will be received during the studyperiod. 11. history of hospitalization within the past 60 days. 12. history of systemic antiviral therapies within the past 30 days. 13. history of oral corticoid steroid use within the past 14 days or steroid injection within the past 6 months. active use of nasal or inhalable steroids is also exclusionary. topical steroids are not exclusionary. 14. has a history of hypersensitivity or severe allergic reaction (e.g., anaphylaxis, generalized urticaria, angioedema, other significant reaction) to nitrites, nitrates, or sun exposure. 15. has any oral abnormality (e.g. ulcer, oral mucositis, gingivitis) that in the opinion of the investigator would interfere with device use, or intra-oral metal body piercings that cannot be removed for the duration of the study. metal orthodontia is permitted as braces will be covered by the device mouthpiece.