The proposed trial will obtain preliminary data on the feasibility of studying RTB101 as compared to placebo for COVID-19 post-exposure prophylaxis in adults age ≥ 65 years to inform the design of a subsequent pivotal trial.

The RTB101-211 study is a Randomized, Double-Blind, Placebo-Controlled Phase 2a Study of RTB101 as COVID-19 Post-Exposure Prophylaxis in Asymptomatic Adults Age ≥65 Years who: have SARS-CoV-2 detected on a surveillance nasal or nasopharyngeal swab OR live in the same house or apartment as someone who has laboratory-confirmed symptomatic COVID-19. The study is designed to obtain study feasibility data for RTB101 in an unbiased fashion and will inform the design of a subsequent pivotal trial.

1. Informed consent must be obtained from the subject before any assessment is performed.

2. Adults (male and female) aged 65 years and over who are asymptomatic but:

   1. have SARS-CoV-2 detected during surveillance nasal or nasopharyngeal swab testing OR
   2. live in the same house or apartment as someone who has laboratory-confirmed symptomatic COVID-19 .

3. Sexually active male subjects with a partner of child-bearing potential must be willing to wear a condom while on study drug and for 1 week after stopping study drug and should not father a child in this period. A condom is required to be used also by vasectomized men with a partner of child-bearing potential to prevent delivery of the drug via seminal fluid.

4. Subject must be able to understand and comply with the requirements of the study including having internet access and an email account, willingness to answer an eDiary questionnaire on a personal electronic device each night, and willingness to answer the telephone questionnaires twice weekly

Exclusion Criteria:

1. Any subject who self-reports:

   1. As a current smoker, or stopped smoking within the past 6 months.
   2. As a previous smoker with a ≥10 pack year smoking history.
   3. Has a household member who currently smokes in the house.

2. Subjects with a medical history of chronic obstructive pulmonary disease (COPD), emphysema or chronic bronchitis requiring active treatment with a prescription medication

3. The subject has already had symptoms consistent with COVID-19 at screening.

4. Subjects who require chronic supplemental oxygen therapy at screening.

5. Subjects with current evidence of an unstable medical disorder including an unstable respiratory disorder, gastrointestinal disorder (including Child-Pugh class B and C hepatic impairment), renal disorder or hematologic disorder (including active leukemia) for which they have had an exacerbation of symptoms within the past month, or are undergoing a change in treatment.

6. The following cardiac conditions:

   1. Unstable angina pectoris
   2. History of myocardial infarction (MI), coronary bypass surgery, or any percutaneous coronary intervention (PCI) within 6 months prior to Screening
   3. Congestive heart failure requiring active treatment with a prescription medication
   4. Unstable or life-threatening cardiac arrhythmia

   a. Chronic stable atrial fibrillation is allowed

7. Subjects with a history of systemic autoimmune diseases (e.g., lupus, inflammatory bowel disease, rheumatoid arthritis, etc.).

   a. Psoriasis confined to the skin and eczema are allowed

8. Subjects receiving immunosuppressive therapy including chronic use of supraphysiologic steroids such as prednisone >10 mg daily (however, inhaled corticosteroids and acute use of higher doses of prednisone to treat conditions such as exacerbation of asthma or other acute conditions are allowed).

9. Subjects with an immunodeficiency disease, including a history of a positive human immunodeficiency virus (HIV) test result.

10. Subjects with a history of gastric bypass surgery.

11. Subjects who require treatment with strong CYP3A4 or CYP1A2 inhibitors or inducers, or subjects who require treatment with digoxin.

12. Use of any other investigational medication or participation in any other investigational study within 5 half-lives of the investigational medication, or within 30 days, whichever is longer; or longer if required by local regulations.