A phase I/II single-blinded, randomised, multi-centre study to determine efficacy, safety and immunogenicity of the candidate Coronavirus Disease (COVID-19) vaccine ChAdOx1 nCoV-19 in UK healthy adult volunteers aged 18-55 years. The vaccine will be administered intramuscularly (IM) into the deltoid region of the arm

There will be 4 study groups and it is anticipated that a total of 1090 volunteers will be enrolled. Volunteers will participate in the study for approximately 12 months from last vaccination visit (approximately 15 months from enrolment for participants receiving 2 doses)

Inclusion Criteria

The volunteer must satisfy all the following criteria to be eligible for the study:

• Healthy adults aged 18-55 years.
• Able and willing (in the Investigator's opinion) to comply with all study requirements (participants must not rely on public transport or taxis).
• Willing to allow the investigators to discuss the volunteer's medical history with their General Practitioner and access all medical records when relevant to study procedures.
• For females only, willingness to practice continuous effective contraception (see below) during the study and a negative pregnancy test on the day(s) of screening and vaccination.
• Agreement to refrain from blood donation during the course of the study.
• Provide written informed consent.

Exclusion Criteria

The volunteer may not enter the study if any of the following apply:

• Planned receipt of any vaccine other than the study intervention within 30 days before and after each study vaccination .with the exception of the licensed seasonal influenza vaccination and the licensed pneumococcal vaccine. Participants will be encouraged to receive this vaccination at least 7 days before or after their study vaccine.
• Prior receipt of an investigational or licensed vaccine likely to impact on interpretation of the trial data (e.g. Adenovirus vectored vaccines, any coronavirus vaccines).
• Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccine candidate.
• Any confirmed or suspected immunosuppressive or immunodeficient state, including HIV infection; asplenia; recurrent severe infections and use of immunosuppressant medication within the past 6 months, except topical steroids or short-term oral steroids (course lasting <14 days) .
• Any autoimmune conditions, except mild psoriasis, well-controlled autoimmune thyroid disease, vitiligo or stable coeliac disease not requiring immunosuppressive or immunomodulatory therapy.
• History of allergic disease or reactions likely to be exacerbated by any component of the ChAdOx1 nCoV-19 or MenACWY vaccines.
• Any history of angioedema .
• Any history of anaphylaxis .
• Pregnancy, lactation or willingness/intention to become pregnant during the study.
• History of cancer (except basal cell carcinoma of the skin and cervical carcinoma in situ).
• History of serious psychiatric condition likely to affect participation in the study (e.g. ongoing severe depression, history of admission to an in-patient psychiatric facility, recent suicidal ideation, history of suicide attempt, bipolar disorder, personality disorder, alcohol and drug dependency, severe eating disorder, psychosis, use of mood stabilisers or antipsychotic medication).
• Bleeding disorder (e.g. factor deficiency, coagulopathy or platelet disorder), or prior history of significant bleeding or bruising following IM injections or venepuncture.
• Any other serious chronic illness requiring hospital specialist supervision.
• Chronic respiratory diseases, including mild asthma (resolved childhood asthma is allowed)
• Chronic cardiovascular disease (including hypertension), gastrointestinal disease, liver disease (except Gilberts Syndrome), renal disease, endocrine disorder (including diabetes) and neurological illness (excluding migraine)
• Seriously overweight (BMI≥40 Kg/m2) or underweight (BMI≤18 Kg/m2)
• Suspected or known current alcohol abuse as defined by an alcohol intake of greater than 42 units every week.
• Suspected or known injecting drug abuse in the 5 years preceding enrolment.
• Any clinically significant abnormal finding on screening biochemistry, haematology blood tests or urinalysis.
• Any other significant disease, disorder or finding which may significantly increase the risk to the volunteer because of participation in the study, affect the ability of the volunteer to participate in the study or impair interpretation of the study data.
• History of laboratory confirmed COVID-19.
• New onset of fever or a cough or shortness of breath or anosmia/ageusia since February 2020. Should a reliable test become available, this exclusion criteria will be replaced with seropositivity for SARS-CoV-2 before enrolment.
• Those who have been at high risk of exposure before enrolment, including but not limited to: close contacts of confirmed COVID-19 cases, anyone who had to self-isolate as a result of a symptomatic household member, frontline healthcare professionals working in A&E, ICU and other higher risk areas. Should a reliable test become available, this exclusion criteria will be replaced with seropositivity for SARS-CoV-2 before enrolment.
• Living in the same household as any vulnerable groups at risk of severe COVID-19 disease (as per Public Health England guidance)

Additional exclusion criteria (subset of participants receiving Paracetamol in group 4 only)

• History of allergic disease or reactions likely to be exacerbated by Paracetamol

Re-vaccination exclusion criteria:

The following AEs associated with any vaccine, or identified on or before the day of vaccination constitute absolute contraindications to further administration of an IMP to the volunteer in question. If any of these events occur during the study, the subject will not be eligible to receive a booster dose and will be followed up by the clinical team or their GP until resolution or stabilisation of the event:

• Anaphylactic reaction following administration of vaccine
• Pregnancy. An exception to this will be prior to receipt of a booster dose at extra visit B. If a pregnant woman has discussed vaccination with their usual clinician (e.g. GP) and chooses to receive a COVID-19 vaccination, this may be administered by the trial team as part of extra visit B or as part of the provision of treatment to controls
• Any AE that in the opinion of the Investigator may affect the safety of the participant or the interpretation of the study results