Inclusion Criteria:

1. Male or female ≥18 years of age. Participation of individuals >60 years will be
limited to ≤ 10/ group.

2. Individuals are willing and able to comply with study requirements, including all
scheduled visits, vaccinations, laboratory tests, and other study procedures.

3. Individuals are willing and able to give an informed consent, prior to screening.

- Individuals who received one of the following vaccination regimens 3 doses of
Pfizer/ Wyeth; 3 doses of AstraZeneca/Fiocruz; or 2 doses of Sinovac/Butantan
and 1 dose of AstraZeneca, or eventually 3 doses of Sinovac/Butantan; or 2
doses of AstraZeneca and 1 dose of Alum/CpG-adjuvanted 9 µg or 30 µg Clover
SCB-2019 vaccine (participants of study TP-SCB-2019-002).

- Interval between last priming dose and 3rd dose minimum 3 months

- Interval between 3rd dose and 4th dose ≥ 4 months

4. Healthy participants or participants with pre-existing medical conditions who are in
a stable medical 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.

5. Female participants are eligible to participate in the study if not pregnant, not
breastfeeding, and at least 1 of the following criteria apply:

- Women of non-childbearing potential;

- Women of childbearing potential (WOCBP) must have a negative urine pregnancy
test prior to study 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 last study vaccination.

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

Exclusion Criteria:

1. Individuals with fever >37.5°C (axillary), or any acute illness at baseline (Day 0)
or within 3 days prior to randomization. Participants meeting this criterion may be
rescheduled within the relevant window. Febrile participants with minor illnesses
can be enrolled at the discretion of the investigator.

2. Individuals who have received more than 3 combined doses of any licensed or
experimental COVID vaccine prior to Day 0 or plan to receive COVID-19 vaccine during
the study period, a drug for COVID-19 prevention or treatment (e.g., drugs,
monoclonal antibodies, such as Rituximab or any other anti-CD20 monoclonal
antibodies during the study period.).

3. Receipt of any authorized or investigational COVID-19 vaccine prior to Day 0 except
for the 03 doses of Pfizer/ Wyeth; 03 doses of AstraZeneca/Fiocruz; or two doses of
Sinovac/Butantan and 01 dose of Pfizer/Wyeth, or eventually 03 doses of
Sinovac/Butantan; or two doses of AstraZeneca and one dose of Clover SCB-2019 ≥ 4
months before enrollment in this study.

4. 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
vaccines (Pfizer/Wyeth, AstraZeneca/Fiocruz, CpG 1018, aluminum, or SCB-2019
components as outlined in the latest summary of product characteristics for
Pfizer/Wyeth, AstraZeneca/Fiocruz and the IB for SCB-2019.

5. Individuals with known bleeding disorder that would, in the opinion of the
investigator, contraindicate intramuscular injection.

6. 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).

7. Individuals with any progressive or severe neurologic disorder, seizure disorder, or
history of Guillain-Barré syndrome.

8. Individuals who received treatment with immunosuppressive therapy in the last 90
days, including cytotoxic agents or systemic corticosteroids, or planned receipt
during the study period. If a short-term course of systemic corticosteroid
immunosuppressive dose has been used for the treatment of acute illness, the
participant should not be included in the study until corticosteroid therapy has
been discontinued for at least 15 days prior to first study vaccination. If the
participant has used an immunosuppressive dose of a depot corticosteroid,
intra-muscular or intra-articular, they must wait 60 days for inclusion in the
study. Inhaled or nebulized, intra-articular, intrabursal, or topical (skin or eyes)
corticosteroids are permitted.

9. Individuals with autoimmune diseases, except: Hashimoto's thyroiditis, vitiligo,
psoriasis, lupus discord and alike; HIV-positive individuals and/or on HIV
treatment.

10. Individuals who have received any other investigational product within 30 days prior
to Day 0 or intend to participate in another clinical study at any time during the
conduct of this study.

11. 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 28 days
after the last vaccination.

12. Individuals who have received treatment with Rituximab or any other anti-CD20
monoclonal antibodies within 9 months prior to Day 0 or planned during the study
period.

13. Administration of intravenous immunoglobulins and/or any blood products within 3
months prior to enrollment or planned administration during the study period.

14. Individuals with any condition that, in the opinion of the investigator, would
interfere with the primary study objectives or pose additional risk to the
participant.

15. Pregnancy.