1. Adult aged ≥18 years or adolescent aged 15 to <18 years and weighing at least 40 kg at the time of Screening. Note: Adolescent enrollment will open only upon sponsor communication to sites after review of Phase 2 data. 2. Tests negative for current or previous SARS-CoV-2 infection by RT-PCR and serology (Cohort B only). Note: Cohort A participants may still be randomized if RT-PCR and serology results are not available by Day 5 of Screening. 3. Is at high risk of SARS-CoV-2 infection as assessed by the Investigator: a) Cohort A (PEP): including, but not limited, to household contact or occupational/recreational exposure to an individual with a diagnosis of SARS-CoV-2 infection (index case).* Note: Participants with recent exposure to a laboratory-confirmed index case must be asymptomatic and randomized within 5 days (120 hours) of collection of the index case’s positive SARS-CoV-2 diagnostic test. * Exposure is generally defined as repeated contact lasting 15 minutes or more within a 24-hour period, where the individuals were within 2 meters (approximately 6.5 feet) of each other, and neither party was wearing a facemask or respirator. b) Cohort B (PrEP): Occupational, housing, recreational and/or social conditions that are likely to increase risk of exposure to SARS-CoV-2 4. Agrees to defer receipt of COVID-19 vaccination for minimum of 180 days (6 months) after dosing. 5. Is able and willing to provide informed consent. A legally authorized representative may be used in cases where inclusion criterion 9 is able to be fulfilled. In the case of adolescents, informed consent/assent must also be obtained as required by local guidelines. 6. Participants assigned female sex at birth who are not of reproductive potential are eligible without requiring the use of contraception and do not require a pregnancy test. This includes female participants who have not undergone menarche or who are documented to be surgically sterile (e.g., hysterectomy, removal of both ovaries, or tubal ligation) or post-menopausal (i.e., amenorrhea >1 year and follicle-stimulating hormone >40 mIU/mL). Follicle-stimulating hormone is not required in post-menopausal females with amenorrhea for >2 years. 7. Participants assigned female sex at birth and who are of childbearing potential may be enrolled in the study if the participant has practiced highly effective contraception or has abstained from all sexual activities that could result in pregnancy for at least 28 days before the day of dosing (Day 1) and has agreed to continue highly effective contraception for sexual activity that could lead to pregnancy through 6 months following dosing. Highly effective contraception for participants assigned female sex at birth is defined as consistent and correct use of a contraceptive as described by the Clinical Trial Facilitation Group (CTFG) and used in accordance with the product label. For example: a) Bilateral tubal ligation b) Intrauterine device. c) Hormonal contraceptive taken or administered via oral (pill), transdermal (patch), intravaginal, implantable, or injectable method. d) Sterilization of a female participant’s male partner before entry into the study. e) Sexual abstinence.* Note: periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods) and withdrawal are not acceptable methods of contraception. *Sexual abstinence is considered an effective method only if defined as refraining from heterosexual intercourse from providing consent until 6 months after dosing. The reliability of sexual abstinence needs to be evaluated in relation to the duration of the study and the preferred and usual lifestyle of the participant. 8. Participants assigned male sex at birth with partner(s) of childbearing potential who agree to use adequate contraception through 6 months after dosing. If their partner is pregnant, males must agree to use a condom. Male participants must also refrain from sperm donation through 6 months after dosing. 9. Able to understand and comply with study requirements/procedures (if applicable, with assistance by caregiver, surrogate, or legally authorized representative) based on the assessment of the Investigator.

1. Adult aged ≥18 years or adolescent aged 15 to <18 years and weighing at least 40 kg at the time of Screening. Note: Adolescent enrollment will open only upon sponsor communication to sites after review of Phase 2 data. 2. Tests negative for current or previous SARS-CoV-2 infection by RT-PCR and serology (Cohort B only). Note: Cohort A participants may still be randomized if RT-PCR and serology results are not available by Day 5 of Screening. 3. Is at high risk of SARS-CoV-2 infection as assessed by the Investigator: a) Cohort A (PEP): including, but not limited, to household contact or occupational/recreational exposure to an individual with a diagnosis of SARS-CoV-2 infection (index case).* Note: Participants with recent exposure to a laboratory-confirmed index case must be asymptomatic and randomized within 5 days (120 hours) of collection of the index case’s positive SARS-CoV-2 diagnostic test. * Exposure is generally defined as repeated contact lasting 15 minutes or more within a 24-hour period, where the individuals were within 2 meters (approximately 6.5 feet) of each other, and neither party was wearing a facemask or respirator. b) Cohort B (PrEP): Occupational, housing, recreational and/or social conditions that are likely to increase risk of exposure to SARS-CoV-2 4. Agrees to defer receipt of COVID-19 vaccination for minimum of 180 days (6 months) after dosing. 5. Is able and willing to provide informed consent. A legally authorized representative may be used in cases where inclusion criterion 9 is able to be fulfilled. In the case of adolescents, informed consent/assent must also be obtained as required by local guidelines. 6. Participants assigned female sex at birth who are not of reproductive potential are eligible without requiring the use of contraception and do not require a pregnancy test. This includes female participants who have not undergone menarche or who are documented to be surgically sterile (e.g., hysterectomy, removal of both ovaries, or tubal ligation) or post-menopausal (i.e., amenorrhea >1 year and follicle-stimulating hormone >40 mIU/mL). Follicle-stimulating hormone is not required in post-menopausal females with amenorrhea for >2 years. 7. Participants assigned female sex at birth and who are of childbearing potential may be enrolled in the study if the participant has practiced highly effective contraception or has abstained from all sexual activities that could result in pregnancy for at least 28 days before the day of dosing (Day 1) and has agreed to continue highly effective contraception for sexual activity that could lead to pregnancy through 6 months following dosing. Highly effective contraception for participants assigned female sex at birth is defined as consistent and correct use of a contraceptive as described by the Clinical Trial Facilitation Group (CTFG) and used in accordance with the product label. For example: a) Bilateral tubal ligation b) Intrauterine device. c) Hormonal contraceptive taken or administered via oral (pill), transdermal (patch), intravaginal, implantable, or injectable method. d) Sterilization of a female participant’s male partner before entry into the study. e) Sexual abstinence.* Note: periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods) and withdrawal are not acceptable methods of contraception. *Sexual abstinence is considered an effective method only if defined as refraining from heterosexual intercourse from providing consent until 6 months after dosing. The reliability of sexual abstinence needs to be evaluated in relation to the duration of the study and the preferred and usual lifestyle of the participant. 8. Participants assigned male sex at birth with partner(s) of childbearing potential who agree to use adequate contraception through 6 months after dosing. If their partner is pregnant, males must agree to use a condom. Male participants must also refrain from sperm donation through 6 months after dosing. 9. Able to understand and comply with study requirements/procedures (if applicable, with assistance by caregiver, surrogate, or legally authorized representative) based on the assessment of the Investigator.