1. Receipt of any vaccine (licensed or investigational) within 30 days before enrolment (1 week for licensed seasonal influenza vaccine or pneumococcal vaccine) 2. Previous receipt of two or more COVID-19 vaccine doses 3. Prior or planned receipt of an investigational or licensed vaccine or product likely to impact on the interpretation of the trial data (e.g. Adenovirus vectored vaccines other than ChAdOx1 nCoV-19) 4. Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccines 5. Any confirmed or suspected immunosuppressive or immunodeficient state, 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) 6. History of anaphylaxis, allergic disease or reactions likely to be exacerbated by any component of study vaccines (e.g. hypersensitivity to the active substance or any of the SmPC-listed ingredients of the Pfizer vaccine), as specified in the UK Immunisation ‘Green Book’ COVID-19 vaccine chapter 7. Pregnancy, lactation or willingness/intention to become pregnant within 3 months post boost vaccine 8. Current diagnosis of or treatment for cancer (except basal cell carcinoma of the skin and cervical carcinoma in situ). This does not include recurrence prophylaxis treatment in those who have no evidence of active disease e.g. hormonal therapy in hormone-sensitive cancers. 9. Bleeding disorder (e.g. factor deficiency, coagulopathy or platelet disorder), or prior history of significant bleeding or bruising following IM injections or venepuncture 10. Continuous use of anticoagulants, such as coumarins and related anticoagulants (i.e. warfarin) or novel oral anticoagulants (i.e. apixaban, rivaroxaban, dabigatran and edoxaban) 11. Suspected or known current alcohol or drug dependency 12. 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 13. Severe and/or uncontrolled cardiovascular disease, respiratory disease, gastrointestinal disease, liver disease, renal disease, rheumatological disease, endocrine disorder and neurological illness (mild/moderate well-controlled comorbidities are allowed) 14. History of active or previous auto-immune neurological disorders (e.g. multiple sclerosis, Guillain-Barre syndrome, transverse myelitis). Bell’s palsy will not be an exclusion criterion 15. History of laboratory-confirmed COVID-19 prior to enrolment (e.g. history of SARS-CoV-2 detection by PCR or antibody to SARS-CoV-2) 16. Significant renal or hepatic impairment 17. Scheduled elective surgery requiring overnight admission and/or general anaesthetic during the trial 18. Participant with a life expectancy of less than 6 months 19. Participants who have participated in another research trial involving an investigational product in the past 12 weeks 20. Insufficient level of English language to undertake all study requirements in the op

1. Receipt of any vaccine (licensed or investigational) within 30 days before enrolment (1 week for licensed seasonal influenza vaccine or pneumococcal vaccine) 2. Previous receipt of two or more COVID-19 vaccine doses 3. Prior or planned receipt of an investigational or licensed vaccine or product likely to impact on the interpretation of the trial data (e.g. Adenovirus vectored vaccines other than ChAdOx1 nCoV-19) 4. Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccines 5. Any confirmed or suspected immunosuppressive or immunodeficient state, 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) 6. History of anaphylaxis, allergic disease or reactions likely to be exacerbated by any component of study vaccines (e.g. hypersensitivity to the active substance or any of the SmPC-listed ingredients of the Pfizer vaccine), as specified in the UK Immunisation ‘Green Book’ COVID-19 vaccine chapter 7. Pregnancy, lactation or willingness/intention to become pregnant within 3 months post boost vaccine 8. Current diagnosis of or treatment for cancer (except basal cell carcinoma of the skin and cervical carcinoma in situ). This does not include recurrence prophylaxis treatment in those who have no evidence of active disease e.g. hormonal therapy in hormone-sensitive cancers. 9. Bleeding disorder (e.g. factor deficiency, coagulopathy or platelet disorder), or prior history of significant bleeding or bruising following IM injections or venepuncture 10. Continuous use of anticoagulants, such as coumarins and related anticoagulants (i.e. warfarin) or novel oral anticoagulants (i.e. apixaban, rivaroxaban, dabigatran and edoxaban) 11. Suspected or known current alcohol or drug dependency 12. 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 13. Severe and/or uncontrolled cardiovascular disease, respiratory disease, gastrointestinal disease, liver disease, renal disease, rheumatological disease, endocrine disorder and neurological illness (mild/moderate well-controlled comorbidities are allowed) 14. History of active or previous auto-immune neurological disorders (e.g. multiple sclerosis, Guillain-Barre syndrome, transverse myelitis). Bell’s palsy will not be an exclusion criterion 15. History of laboratory-confirmed COVID-19 prior to enrolment (e.g. history of SARS-CoV-2 detection by PCR or antibody to SARS-CoV-2) 16. Significant renal or hepatic impairment 17. Scheduled elective surgery requiring overnight admission and/or general anaesthetic during the trial 18. Participant with a life expectancy of less than 6 months 19. Participants who have participated in another research trial involving an investigational product in the past 12 weeks 20. Insufficient level of English language to undertake all study requirements in the op