1. rapidly deteriorating or likely to require escalation to high flow oxygen, invasive or non-invasive ventilatory support within 24 hours according to investigator's opinion. 2. unable to safely receive a nebulized treatment for approximately 8 minutes according to investigator's opinion. 3. unable to receive or considered ineligible for invasive or non-invasive ventilatory support. 4. history of methemoglobinemia. 5. presence of uncontrolled asthma, history of severe bronchospasm. 6. presence of severe chronic respiratory disease and tracheostomy. 7. suspected or confirmed untreated, active tuberculosis. 8. severely immune-compromised participants in investigator's opinion. 9. recent active coronary artery disease or decompensated heart failure.

1. rapidly deteriorating or likely to require escalation to high flow oxygen, invasive or non-invasive ventilatory support within 24 hours according to investigator's opinion. 2. unable to safely receive a nebulized treatment for approximately 8 minutes according to investigator's opinion. 3. unable to receive or considered ineligible for invasive or non-invasive ventilatory support. 4. history of methemoglobinemia. 5. presence of uncontrolled asthma, history of severe bronchospasm. 6. presence of severe chronic respiratory disease and tracheostomy. 7. suspected or confirmed untreated, active tuberculosis. 8. severely immune-compromised participants in investigator's opinion. 9. recent active coronary artery disease or decompensated heart failure.

rapidly deteriorating or likely to require escalation to high flow oxygen, invasive or non-invasive ventilatory support within 24 hours according to investigator's opinion. unable to safely receive a nebulized treatment for approximately 8 minutes according to investigator's opinion. unable to receive or considered ineligible for invasive or non-invasive ventilatory support. history of methemoglobinemia. presence of uncontrolled asthma, history of severe bronchospasm. presence of severe chronic respiratory disease and tracheostomy. suspected or confirmed untreated, active tuberculosis. severely immune-compromised participants in investigator's opinion. recent active coronary artery disease or decompensated heart failure.

rapidly deteriorating or likely to require escalation to high flow oxygen, invasive or non-invasive ventilatory support within 24 hours according to investigator's opinion. unable to safely receive a nebulized treatment for approximately 8 minutes according to investigator's opinion. unable to receive or considered ineligible for invasive or non-invasive ventilatory support. history of methemoglobinemia. presence of uncontrolled asthma, history of severe bronchospasm. presence of severe chronic respiratory disease and tracheostomy. suspected or confirmed untreated, active tuberculosis. severely immune-compromised participants in investigator's opinion. recent active coronary artery disease or decompensated heart failure.

1. rapidly deteriorating or likely to require escalation to high flow oxygen, invasive or non-invasive ventilatory support within 24 hours according to investigator's opinion. 2. unable to safely receive a nebulized treatment for approximately 8 minutes according to investigator's opinion. 3. unable to receive or considered ineligible for invasive or non-invasive ventilatory support. 4. history of methemoglobinemia. 5. presence of uncontrolled asthma, history of severe bronchospasm. 6. presence of severe chronic respiratory disease and tracheostomy. 7. suspected or confirmed untreated, active tuberculosis. 8. severely immune-compromised participants in investigator's opinion. 9. recent active coronary artery disease or decompensated heart failure.

1. rapidly deteriorating or likely to require escalation to high flow oxygen, invasive or non-invasive ventilatory support within 24 hours according to investigator's opinion. 2. unable to safely receive a nebulized treatment for approximately 8 minutes according to investigator's opinion. 3. unable to receive or considered ineligible for invasive or non-invasive ventilatory support. 4. history of methemoglobinemia. 5. presence of uncontrolled asthma, history of severe bronchospasm. 6. presence of severe chronic respiratory disease and tracheostomy. 7. suspected or confirmed untreated, active tuberculosis. 8. severely immune-compromised participants in investigator's opinion. 9. recent active coronary artery disease or decompensated heart failure.

1. rapidly deteriorating or likely to require escalation to high flow oxygen, invasive or non-invasive ventilatory support within 24 hours according to investigator's opinion. 2. unable to safely receive a nebulized treatment for approximately 4 minutes according to investigator's opinion. 3. unable to receive or considered ineligible for invasive or non-invasive ventilatory support. 4. history of methemoglobinemia. 5. presence of uncontrolled asthma, history of severe bronchospasm. 6. presence of severe chronic respiratory disease and tracheostomy. 7. suspected or confirmed untreated, active tuberculosis. 8. severely immune-compromised participants in investigator's opinion. 9. recent active coronary artery disease or decompensated heart failure.

1. rapidly deteriorating or likely to require escalation to high flow oxygen, invasive or non-invasive ventilatory support within 24 hours according to investigator's opinion. 2. unable to safely receive a nebulized treatment for approximately 4 minutes according to investigator's opinion. 3. unable to receive or considered ineligible for invasive or non-invasive ventilatory support. 4. history of methemoglobinemia. 5. presence of uncontrolled asthma, history of severe bronchospasm. 6. presence of severe chronic respiratory disease and tracheostomy. 7. suspected or confirmed untreated, active tuberculosis. 8. severely immune-compromised participants in investigator's opinion. 9. recent active coronary artery disease or decompensated heart failure.