Inclusion Criteria:

Subjects enrolled in the trial must meet all of the following criteria.

* Confirmed COVID-19 pneumonia
* Hypoxia as defined by room air oxygen saturation less than 92% or supplemental oxygen requirement
* Presence of at least one additional biomarker that has been shown to predict poor prognosis: a) serum ferritin ≥500ug/l, b) LDH ≥250U/L, c) d-dimer ≥1ug/L, or d) lymphopenia as defined by absolute lymphocyte count <1,000/uL
* Age ≥ 18 years
* Completed informed consent

Exclusion Criteria:

Subjects who meet ANY of the following criteria are not eligible for enrollment as study participants:

* Known allergy or hypersensitivity to sirolimus
* Inability or refusal to provide informed consent
* Advanced respiratory support (high flow oxygen ≥ 15 L/min, CPAP, non-invasive or invasive mechanical ventilation)
* Active enrollment in other interventional clinical drug trials. Co-enrollment in observational studies and biorepositories is allowed.
* Pregnant women
* Breast feeding
* On chronic immunosuppression for other medical conditions such as rheumatological disorders, inflammatory bowel disease, or in patients with organ transplants. A list of these medications is provided in Section 12.3.4
* Any clinically significant medical disease which in the opinion of the investigator precludes the patient from enrolling in the trial, including (but not limited to):

* History of liver cirrhosis
* End stage renal disease or need for renal replacement therapy
* Decompensated heart failure
* Known active tuberculosis or history of incompletely treated tuberculosis
* Uncontrolled systemic bacterial or fungal infections
* Active viral infection other than COVID-19