Leidos-Enabled Adaptive Protocol for Clinical Trials (LEAP-CT) in Hospitalized Patients With COVID-19 (Addendum 1)

Inclusion Criteria: * Male or female participants must be at least 18 years of age, inclusive, at the time of signing the informed consent form. * Confirmed COVID-19 or symptom onset within 7 days of hospitalization, as shown by medical history, physical exam, and laboratory tests (PCR), and who have been hospitalized for COVID-19 at WHO Grade 4-5. * Contraceptive use by men or women should be consistent with Appendix 4 of the Master Protocol (LDOS-21-001). * Capable of understanding and providing a signed informed consent form. * Reliable access to the internet. Exclusion Criteria: Participants are excluded from the study if any of the following criteria apply: * Pregnant or breastfeeding * History of HIV * Ongoing treatment that cannot be temporarily discontinued during the study: anti-inflammatory treatment (nonsteroidal anti-inflammatory drugs \[NSAIDS\]);corticosteroids; antimalarials; antiarrhythmics; tricyclic antidepressants; natalizumab; quinolones; macrolides; and agalsidase alfa and beta 1. drugs dependent on gastric pH for absorption, e.g., dasatinib, delavirdine, mesylate, cefditoren, and fosamprenavir; 2. tizanidine (CYP1A2) substrate; 3. drugs that interfere with hemostasis (e.g., warfarin, aspirin, selective serotonin reuptake inhibitors \[SSRIs\]/serotonin norepinephrine reuptake inhibitors \[SNRIs\]); 4. angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARB), or beta-blockers; 5. diuretics; 6. digoxin * Ongoing famotidine, celecoxib, or other COVID-19 clinical investigational treatment(s) within the past 30 days or current participation in another investigational clinical trial * History of immunosuppression * History of asthma, urticaria, or other allergic-type reactions after taking aspirin or other NSAIDs * Rejection of participation at the discretion of the Principal Investigator or Sponsor * Any contraindication for famotidine or celecoxib treatment: a. Famotidine or celecoxib hypersensitivity; b. Retinopathy, visual field or visual acuity disturbances; c. History of cardiovascular disease, such as congestive heart failure, QT prolongation, bradycardia (\<50 bpm), ventricular tachycardia, other arrhythmias, as determined at screening electrocardiogram (ECG) or medical history; d. Potassium \<3 mEq/L (milliequivalent/liter) as determined at Visit 1; e. Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \>5 upper normal limit, as determined at Visit 1; f. Previous myocardial infarction; e. Myasthenia gravis; h. Psoriasis or porphyria; i. Glomerular clearance, 60 mL/min; j. Previous history of severe hypoglycemia; k. Known or suspected to be poor CYP2C9 metabolizers based on genotype or previous history or experience with other CYP2C9 substrates, such as warfarin and phenytoin; l. Moderate or severe hepatic impairment, e.g., Child-Pugh Class B or C.