A Study of a Candidate COVID-19 Vaccine (COV003)

Inclusion Criteria: * Adults from 18 to 55 years of age * Adults aged 56-69 years old (after review of safety data by DSMB in this age group in the UK trial) * Adults aged 70 and above years old (after review of safety data by DSMB in this age group in the UK trial) * Able and willing (in the Investigator's opinion) to fulfill all study requirements; * Health professionals and adults at high risk of exposure to SARS-CoV-2, as defined in section 5.2 of this protocol; * Serology with SARS-CoV-2 negative IgG antibodies; This inclusion criteria does not apply to participants enrolled from version 4.0 of the protocol onwards. * Willing to allow investigators to discuss the participant's clinical history with their GP/personal physician and access medical records relevant to the study procedures * Only for women of childbearing age willing to practice continuous effective birth control (see below) during the study, and a negative pregnancy test on the screening and vaccination day(s); * Consent to abstain from blood donation during the course of the study; * Provide informed consent in writing Exclusion Criteria: * Participation in trials of prophylactic drugs for COVID-19 during the course of the study; Note: Participation in COVID-19 treatment trials is permitted in case of hospitalization due to COVID-19, after confirmation of positive PCR. The study team should be informed as soon as possible. Participants with COVID-19 not hospitalized with positive PCR results for COVID-19 may be medicated according to standard clinical practice. * Participation in SARS-CoV-2 serological research where participants are informed of their serological status during the course of the study; * Planned receipt of any vaccine (authorized or investigational), within 30 days before and after vaccination; * Prior receipt of an investigational vaccine or authorized with the possibility of impacting the interpretation of the study data (for example, vaccines vectorized by Adenovirus, any vaccines against coronavirus); * Administration of immunoglobulins and/or any blood products in the three months prior to the planned administration of the candidate vaccine; * Any confirmed or suspected immunosuppressive or immunodeficiency state; asplenia; severe recurrent infections and chronic use (more than 14 days) of immunosuppressive medication in the last 6 months, except for topical steroids or short-term oral steroids (cycle lasting ≤14 days); * History of allergic disease or reactions possibly exacerbated by any component of ChAdOx1 nCoV-19 or MenACWY or paracetamol; * Any history of angioedema; * Any history of anaphylaxis; * Pregnancy, lactation or willingness/intention to become pregnant during the study; * Current diagnosis or treatment for cancer (except basal cell carcinoma of the skin and cervical carcinoma in situ); * History of severe psychiatric illness that possibly affects your participation in the study; * Hemorrhagic disorder (for example, factor deficiency, coagulopathy or platelet disorder), or a previous history of significant bleeding or bruising after IM injections or venipuncture; * Current suspected or known dependence on alcohol or drugs; * Severe and/or uncontrolled cardiovascular diseases, respiratory diseases, gastrointestinal diseases, liver disease, kidney disease, endocrine disorder, and neurological disease (mild/moderate well-controlled comorbidities are allowed); * History of COVID-19 confirmed by laboratory; * Seropositive for antibodies to SARS-CoV-2 before recruitment; This exclusion criteria does not apply to participants enrolled from version 4.0 of the protocol onwards * Continued use of anticoagulants, such as coumarins and related anticoagulants (for example, warfarin) or new oral anticoagulants (for example, apixaban, rivaroxaban, dabigatran and edoxaban); * Any other significant illness, disorder or finding that may significantly increase the risk for the participant, affect his/her ability to participate in the study or impair the interpretation of the study data. Re-vaccination exclusion criteria (two-dose groups only) * Anaphylactic reaction following administration of vaccine * Pregnancy