Assessment of Immunogenicity, Safety and Reactogenicity of a Booster Dose of Various COVID-19 Vaccine Platforms in Individuals Primed With Several Regimes.

Inclusion Criteria: 1. Male or female ≥18 years of age. 2. Individuals are willing and able to comply with study requirements, including all scheduled visits, vaccination, laboratory tests, and other study procedures. 3. Individuals are willing and able to give an informed consent, prior to screening. 4. Individuals must have completed vaccine priming, regardless of vaccine regimen. Primary vaccination and previous booster scheme data will be annotated as patient history. 5. Interval between last dose and current study dose of a minimum of 4 months and a maximum of 24 months (to optimize candidate participation). 6. 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. 7. 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 during the study, until 90 days after the study vaccination. Exclusion Criteria: Participants are excluded from the study if any of the following criteria apply: 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. Self-reported confirmed COVID-19 infection, through RT-PCR or lateral flow test, in the last 4 weeks. 3. Individuals who did not complete the primary vaccination scheme for any licensed COVID vaccine or plan to receive another COVID-19 vaccine (other than the study vaccines) 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.). 4. Individuals who have a history of severe adverse reaction associated with a vaccine or severe allergic reaction (e.g., anaphylaxis, venal or arterial thrombosis, thrombocytopenia) 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/Clover). 5. Individuals with capillary leakage syndrome or thrombosis with thrombocytopenia syndrome \- TTS (possibly associated with vaccination with the AstraZeneca/Fiocruz vaccine). 6. Individuals who had pericarditis or myocarditis (these pathologies may be associated with the Pfizer/Wyeth vaccine, especially in young men). 7. Individuals with known bleeding disorder that, in the opinion of the investigator, contraindicate intramuscular injection. 8. 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). 9. Individuals with any progressive or severe neurologic disorder, seizure disorder, or history of Guillain-Barré syndrome. 10. 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 nebulized, intra-articular, intrabursal, or topical (skin or eyes) corticosteroids are permitted. 11. Individuals with autoimmune diseases, except: Hashimoto's thyroiditis, vitiligo, psoriasis, lupus discord and alike; HIV-positive individuals and/or on HIV treatment. 12. 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. 13. 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. 14. 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. 15. Administration of intravenous immunoglobulins and/or any blood products within 3 months prior to enrollment or planned administration during the study period. 16. 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. 17. Pregnancy. 18. Breastfeeding.