• At the time of randomization, requires supplemental oxygen ≥2 LPM due to hypoxemia.

• Immunocompromised, as defined by one or more of the following:

‣ Received an autologous or allogeneic hematopoietic stem cell transplantation (HSCT) at any time in the past

⁃ Received a solid organ transplant at any time in the past

⁃ Has been or is currently being treated with chemotherapy for hematologic malignancies (e.g., leukemia, myeloma, lymphoma) and/or solid tumor malignancies (e.g., lung, breast, brain cancer) at any time in the past

⁃ Has an immunodeficiency due to congenital abnormality (only applicable to subjects age \< 18 years old) or pre-term birth (only applicable to subjects age ≤ 2 years old)

• Has, within 3 days prior to randomization, a confirmed LRTI with a sialic acid dependent respiratory virus

• If female, subject must meet one of the following conditions:

‣ Not be of childbearing potential or

⁃ Be of childbearing potential and have a negative urine/serum pregnancy test and agrees to practice an acceptable method of contraception

• Non-vasectomized males are required to practice effective birth control methods

• Capable of understanding and complying with procedures as outlined in the protocol

• Provides signed informed consent prior to the initiation of any screening or study-specific procedures

∙ For COVID-19 sub study:

• Be ≥18 years of age

• Provide adequate medical history to permit accurate stratification (but health status may be healthy, high-risk conditions, or immunocompromised).

• Prior to SARS CoV 2 infection, has the ability to carry out self-care activities of daily living (basic ADL)

• Have lower respiratory tract infection (LRTI) confirmed by CT imaging, with or without contrast, to involve at least 2 lobes of the lung.

• Has laboratory-confirmation of the presence of SARS CoV 2 in the respiratory tract by at least one of the following samples

• Satisfy inclusion criteria #1, 4, 5, 6, 7 of the main study