Leidos-Enabled Adaptive Protocol (LEAP-CT) for Evaluation of Post-exposure Prophylaxis for Newly-infected COVID-19 Patients

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 SARS-CoV-2 polymerase chain reaction (PCR) positive patient within 5 days of enrollment, as shown by medical history and reported PCR test result. * Reports having one or more symptoms consistent with SARS-CoV-2, as defined in Master Protocol Appendix 3 Table 4. * COVID-19 diagnosis must be WHO grade ≤3. * Contraceptive use by men or women should be consistent with Appendix 4 of the Master protocol (LDOS-21-001). * Reliable access to the Internet via a browser installed on personal device or computer. * Capable of understanding and providing signed informed consent. Exclusion Criteria: * Pregnancy or breastfeeding * Ongoing antiviral or antiretroviral treatment * Known history of HIV * Ongoing anti-inflammatory treatment that cannot be temporarily discontinued during the study. This includes nonsteroidal anti-inflammatory drugs (NSAIDs), and corticosteroids - including Dexamethasone (dexamethasone administration restricted to recommended standard of care use per NIH COVID-19 Guidelines) 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 treatment that cannot be temporarily discontinued during the study, with: antimalarials, antiarrhythmics, tricyclic antidepressants, natalizumab, quinolones, macrolides, agalsidase alfa and beta * Ongoing famotidine or celecoxib or other COVID-19 clinical investigational treatment(s) within the past 30 days, or current participation in another investigational clinical trial * History of asthma, urticaria, or other allergic-type reactions after taking aspirin or other NSAIDs * History of immunosuppression * Rejection of participation by Principal Investigator or Sponsor * Any contraindication for famotidine or celecoxib treatment: 1. Famotidine or celecoxib hypersensitivity 2. Retinopathy, visual field or visual acuity disturbances 3. History of cardiovascular disease, such as congestive heart failure, QT prolongation, myocardial infarction, bradycardia (\<50 bpm), ventricular tachycardia, other arrhythmias 4. Myasthenia gravis 5. Psoriasis or porphyria 6. History of renal failure/dialysis or a glomerular clearance \<60 mL/min 7. History of severe hypoglycemia 8. Moderate or severe hepatic impairment, e.g., Child-Pugh Class B or C 9. 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