The purpose of this double-blind, randomized, controlled study is to evaluate the efficacy, immunogenicity, reactogenicity and safety of an adjuvanted recombinant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) trimeric spike (S)-protein subunit vaccine (SCB-2019) for the prevention of SARS-CoV-2-mediated COVID-19 in Participants Aged 12 Years and Older.

This study will assess the efficacy against COVID-19, immunogenicity, reactogenicity, and safety of CpG 1018/Alum-adjuvated SCB-2019 vaccine. The COVID-19 pandemic has resulted in high morbidity and mortality, caused major disruption to healthcare systems, and has had significant socioeconomic impacts. Currently, only limited treatment options are available against COVID-19 and accelerated vaccine development is urgently needed. Several COVID-19 vaccines were recently authorized in some countries, but the global supply is insufficient for pandemic control. Additional safe and effective vaccines for COVID-19 prevention would have significant public health impact.

Placebo recipients will be offered two doses of SCB-2019 vaccine at defined points as part of the study.

Adults participants who received SCB-2019 vaccine, will be given a third dose of the SCB-2019 vaccine at least 4 months after the second dose to assess the safety and efficacy of a booster (third) dose.

Inclusion Criteria:

1. Male or females ≥12 years of age, inclusive*.

2. Participants who are willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, the electronic completion of the COVID-19 ePRO and other study procedures.

3. Healthy adult or adolescent subjects or adult or adolescent subjects 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.

   *Note: The first 200 individuals enrolled in the Phase 2 part of the study should be healthy subjects 18 to 64 years or age without comorbidities associated with a high risk of severe COVID-19

4. Female subjects who are WOCBP are eligible to participate in the study if not pregnant, not breastfeeding, and at least 1 of the following criteria apply:

   • WOCBP must have a negative urine pregnancy test prior to each vaccination. A confirmatory serum pregnancy test may be conducted at the investigator's discretion.
   • They must be using a highly effective licensed method of birth control for 30 days prior to the first vaccination and must agree to continue such precautions during the study until 90 days after the second vaccination.

5. Male subjects must agree to employ acceptable contraception from the day of first dose of the study vaccine/placebo until 6 months after the last dose of the study vaccine/placebo and also refrain from donating sperm during this period.

6. Individuals (or their legally acceptable representative based on local regulations) willing and able to give an informed consent, prior to screening. For adolescent subjects: informed assent signed by adolescents and informed consent signed by the parent(s) or legally acceptable representative(s) as per local requirements.

7. Applicable for HIV-positive individuals only if:

They are medically stable at screening, as determined by the investigator, and free of opportunistic infections in the 1 year prior to first study vaccination, and They have an HIV-1 viral load <1000 copies/mL within 45 days of randomization in the study, and They are receiving highly active antiretroviral therapy (HAART) for at least 3 months before screening. Changes in antiretroviral dosage within 3 months of entering the study are allowed, as are exchanges in pharmacological formulations.

Exclusion Criteria:

1. Individuals with laboratory-confirmed SARS-CoV-2 infection (e.g., a positive RT-PCR* or Rapid COVID-19 Antigen test) at screening or within 14 days prior to enrollment.
2. Individuals with behavioral or cognitive impairment (including drug and alcohol abuse) in the opinion of the investigator.
3. Individuals with any progressive or severe neurologic disorder, seizure disorder, or history of Guillian-Barré syndrome.
4. Individuals who receive treatment with immunosuppressive therapy, including cytotoxic agents or systemic corticosteroids, e.g., for cancer or an autoimmune disease, or planned receipt during the study period.
5. Individuals who are pregnant, or breastfeeding, or planning to become pregnant during the study period.
6. Individuals who have a history of severe adverse reaction associated with a vaccine or severe allergic reaction (e.g., anaphylaxis) to any component of the study vaccine (SCB-2019, CpG1018 Adjuvant and Aluminum hydroxide components).
7. Individuals who have a history of malignancy within 1 year before screening (exceptions are squamous and basal cell carcinomas of the skin and carcinoma in situ of the cervix which have been cured, or other malignancies with minimal risk of recurrence).
8. Individuals who have received any other investigational product within 30 days prior to Day 1 or intent to participate in another clinical study at any time during the conduct of this study.
9. Individuals who have received previous vaccination with any coronavirus vaccine.
10. Individuals who have received any other licensed vaccines within 14 days prior to enrollment in this study or who are planning to receive any vaccine up to 14 days after the second vaccination.
11. Individuals with known bleeding disorder that would, in the opinion of the investigator, contraindicate intramuscular injection.
12. Individuals who received any blood/plasma products or immunoglobulins within 60 days prior to Day 1 or plan to receive it during the study period.
13. Individuals with any condition that, in the opinion of the investigator, may increase the risk of study participation or interfere with the assessment of the primary study objectives.
14. Individuals with fever >37.8°C (irrespective of method), or any acute illness at baseline (Day 1) or within 3 days of randomization.