Phase 3 Study of S-217622 in Prevention of Symptomatic SARS-CoV-2 Infection

Inclusion Criteria:

Index Participants

Only 1 index participant from each household will be enrolled in the study. Participants are eligible to be included as an index participant if all of the following criteria apply:

1. Pediatric participants or adult participants (of any age)

2. The index participant must:

3. Have at least 1 COVID-19 symptom within 24 hours before the index participantproviding informed consent. COVID-19 symptom(s) must be deemed by theinvestigator as related to the current SARS-CoV-2 infection (not related topreexisting comorbidities) or deemed as preexisting and worsened due toSARS-CoV-2 infection.

4. Must have positive SARS-CoV-2 test (a nucleic acid amplification test orantigen test) from any respiratory tract specimen from a sample collected priorto randomization of the participant

5. Must have a potential study participant who can participate in the study after onsetof COVID-19 symptoms in an index participant

Study Participants

Multiple study participants from the same household are allowed to be enrolled in the study. The study intervention randomization will be performed based at the study participant's level. Participants will be eligible to be included in the study only if all of the following criteria apply:

1. ≥ 12 years of age at the time of signing the informed consent

2. Has a negative screening for SARS-CoV-2 infection, as determined by SARS-CoV-2 test (a nucleic acid amplification test or antigen test) from any respiratory tractspecimen (for example, oropharyngeal, nasopharyngeal or nasal swab, or saliva).

3. Has lived in household with index participant and will continue to live in samehousehold and share common areas such as dining rooms and bathrooms until the end ofthe study

4. Must not be considered by the investigator or subinvestigator to have SARS-CoV-2infection and:

5. No measured fever at Screening (defined as body temperature ≥ 38.0°Celsius [C]per tympanic or rectal thermometer or ≥ 37.5°C per axillary, oral, orforehead/temporal thermometer)

6. No COVID-19 symptoms at Screening (if a participant has COVID-19-like symptomscaused by comorbidities, only 1 symptom will be allowed)

7. Capable and willing to complete a participant diary

8. a. Male participants: Participants with partners that are woman of childbearingpotential (WOCBP) must agree to use effective contraception. Participants withpregnant partners must agree to use effective contraception. b. Female participants: A female participant is eligible to participate if she isnot pregnant or breastfeeding, and the following conditions applies:

• Is not a WOCBP or

• All of the following apply:

• Is a WOCBP and using a contraceptive method that is effective as describedin the protocol.

• A WOCBP must have a negative urine pregnancy test within 24 hours beforethe first dose of study intervention period.

• If a urine pregnancy test cannot be confirmed as negative (for example, anambiguous result), a serum pregnancy test must be negative.

• Additional requirements for pregnancy testing during and after studyintervention as described in the protocol.

• The investigator/subinvestigator will review medical history, menstrualhistory, and recent sexual activity to decrease the risk of inclusion of awoman with an early undetected pregnancy.

7. Participant must be randomized ≤ 72 hours from onset of COVID-19 symptoms in theindex participant.

Exclusion Criteria:

Study Participants: Participants will be excluded from the study if any of the following criteria apply:

1. Tested positive for SARS-CoV-2 in the past 6 months.

2. Have an underlying disease requiring systemic corticosteroids (excluding topical),antipyretics/analgesics, or immunosuppressive agents.

3. Known current renal impairment defined as creatinine clearance < 30milliliters/minute by Cockcroft Gault or requiring dialysis.

4. Participants with severe liver dysfunction, such as known history of cirrhosis orliver decompensation (including ascites, variceal bleeding, or hepaticencephalopathy).

5. Received approved, authorized, or investigational convalescent plasma, or otheranti- SARS-CoV-2 biologic products within 3 months of the Screening Visit

6. Received approved, authorized, or investigational anti-SARS-CoV-2 monoclonalantibodies (mAbs) in the last 6 months.

7. Received any SARS-CoV-2 vaccine within 6 months prior to the Screening Visit or isexpected to receive a SARS-CoV-2 vaccine or other approved, authorized, orinvestigational postexposure prophylaxis treatments until the end of the study.

8. Participants who have used any of the following drugs within 14 days prior toenrollment:

9. Strong cytochrome P450 (CYP) 3A inducer

10. Products containing St. John's wort

11. Exposed to an investigational drug within 30 days or 5 half-lives of the drug priorto the Screening Visit.

12. Positive urine pregnancy test at Screening Visit or are lactating.

13. Known allergy/sensitivity or any hypersensitivity to components of S-217622 orplacebo for S-217622.

14. Any condition or circumstance that, in the opinion of the investigator orsubinvestigator, would compromise the safety of the participant or the quality ofthe study data.

Note: Other protocol-defined Inclusion/Exclusion criteria may apply.