A Phase 3 Randomized Double Blind Efficacy and Safety Study of Oral Polio Vaccine and NA-831 for Covid-19

Inclusion Criteria:

- Participants who are at high risk of SARS-CoV-2 infection, defined as adults whose
locations or circumstances put them at appreciable risk of exposure to SARS-CoV-2 and
COVID-19.

- Understands and agrees to comply with the study procedures and provides written
informed consent.

- Able to comply with study procedures based on the assessment of the Investigator.

- Female participants of non-childbearing potential may be enrolled in the study.
Non-childbearing potential is defined as surgically sterile (history of bilateral
tubal ligation, bilateral oophorectomy, hysterectomy) or postmenopausal (defined as
amenorrhea for ≥12 consecutive months prior to Screening without an alternative
medical cause). A follicle-stimulating hormone (FSH) level may be measured at the
discretion of the Investigator to confirm postmenopausal status.

- Female participants of childbearing potential may be enrolled in the study if the
participant fulfills all the following criteria:

- Has a negative pregnancy test at Screening and on the day of the first dose (Day
1).

- Has practiced adequate contraception or has abstained from all activities that
could result in pregnancy for at least 28 days prior to the first dose (Day 1).

- Has agreed to continue adequate contraception through 3 months following the
second dose on Day 29.

- Is not currently breastfeeding.

- Male participants engaging in activity that could result in pregnancy of sexual
partners must agree to practice adequate contraception and refrain from sperm donation
from the time of the first dose and through 3 months after the second dose.

- Healthy adults or adults with pre-existing medical conditions who are in stable
condition. A stable medical condition is defined as disease not requiring significant
change in therapy or hospitalization for worsening disease during the 3 months before
enrollment.

Exclusion Criteria:

- Is acutely ill or febrile 72 hours prior to or at Screening. Fever is defined as a
body temperature ≥38.0°C/100.4°F. Participants meeting this criterion may be
rescheduled within the relevant window periods. Afebrile participants with minor
illnesses can be enrolled at the discretion of the Investigator.

- Is pregnant or breastfeeding.

- Known history of SARS-CoV-2 infection.

- Prior administration of an investigational coronavirus (SARS-CoV, Middle East
Respiratory Syndrome [MERS]-CoV) vaccine or current/planned simultaneous participation
in another interventional study to prevent or treat COVID-19.

- Demonstrated inability to comply with the study procedures.

- An immediate family member or household member of this study's personnel.

- History of anaphylaxis, urticaria, or other significant adverse reaction requiring
medical intervention after receipt of a vaccine.

- Bleeding disorder considered a contraindication to intramuscular injection or
phlebotomy.

- Has received or plans to receive a vaccine within 28 days prior to the first dose (Day
1) or plans to receive a non-study vaccine within 28 days prior to or after any dose
of investigational product (except for seasonal influenza vaccine).

- Has participated in an interventional clinical study within 28 days prior to the day
of enrollment.

- Immunosuppressive or immunodeficient state, including human immunodeficiency virus
(HIV) infection, asplenia, and recurrent severe infections.

- Has received systemic immunosuppressants or immune-modifying drugs for >14 days in
total within 6 months prior to Screening (for corticosteroids ≥20 milligram (mg)/day
of prednisone equivalent). Topical tacrolimus is allowed if not used within 14 days
prior to Screening.

- Has received systemic immunoglobulins or blood products within 3 months prior to the
day of Screening.

- Has donated ≥450 milliliters (mL) of blood products within 28 days prior to Screening.