1. Receipt of any vaccine (licensed or investigational) other than the study intervention within 30 days before and after each study vaccination (one week for licensed seasonal influenza vaccine or pneumococcal vaccine) 2. 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, any coronavirus vaccines) 3. Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccines 4. Any confirmed or suspected immunosuppressive or immunodeficient state, asplenia, recurrent severe infections, or use of immunosuppressant medication within the past 6 months, with the exception of topical steroids or short-term oral steroids (course lasting =14 days) 5. History of 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) 6. Any history of anaphylaxis 7. Pregnancy, lactation, or willingness/intention to become pregnant within 3 months post boost vaccine 8. Current diagnosis of or treatment for cancer (with the exception of basal cell carcinoma of the skin and cervical carcinoma in situ) 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, 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 (history of SARS-CoV-2 detection by PCR or antibody to SARS-CoV-2) 16. Significant renal or hepatic impairment 17. Scheduled elective surgery during the trial 18. Life expectancy of <6 months 19. Participation 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 opinion of the Investigators 21. If at Visit 1 Screening & Vaccination the volunteer has either of the following, they will not be enrolled that day, however, they may be considered for enrolment later in the trial, if they recover in sufficient time: 21.1. Acute respiratory illness (m

1. Receipt of any vaccine (licensed or investigational) other than the study intervention within 30 days before and after each study vaccination (one week for licensed seasonal influenza vaccine or pneumococcal vaccine) 2. 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, any coronavirus vaccines) 3. Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccines 4. Any confirmed or suspected immunosuppressive or immunodeficient state, asplenia, recurrent severe infections, or use of immunosuppressant medication within the past 6 months, with the exception of topical steroids or short-term oral steroids (course lasting =14 days) 5. History of 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) 6. Any history of anaphylaxis 7. Pregnancy, lactation, or willingness/intention to become pregnant within 3 months post boost vaccine 8. Current diagnosis of or treatment for cancer (with the exception of basal cell carcinoma of the skin and cervical carcinoma in situ) 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, 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 (history of SARS-CoV-2 detection by PCR or antibody to SARS-CoV-2) 16. Significant renal or hepatic impairment 17. Scheduled elective surgery during the trial 18. Life expectancy of <6 months 19. Participation 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 opinion of the Investigators 21. If at Visit 1 Screening & Vaccination the volunteer has either of the following, they will not be enrolled that day, however, they may be considered for enrolment later in the trial, if they recover in sufficient time: 21.1. Acute respiratory illness (m

1. Receipt of any vaccine (licensed or investigational) other than the study intervention within 30 days before and after each study vaccination (one week for licensed seasonal influenza vaccine or pneumococcal vaccine)2. 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, any coronavirus vaccines)3. Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccines4. Any confirmed or suspected immunosuppressive or immunodeficient state, asplenia, recurrent severe infections, or use of immunosuppressant medication within the past 6 months, with the exception of topical steroids or short-term oral steroids (course lasting =14 days)5. History of 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)6. Any history of anaphylaxis 7. Pregnancy, lactation, or willingness/intention to become pregnant within 3 months post boost vaccine8. Current diagnosis of or treatment for cancer (with the exception of basal cell carcinoma of the skin and cervical carcinoma in situ) 9. Bleeding disorder (e.g. factor deficiency, coagulopathy, or platelet disorder), or prior history of significant bleeding or bruising following IM injections or venepuncture10. 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 dependency12. 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 data13. Severe and/or uncontrolled cardiovascular disease, respiratory disease, gastrointestinal disease, liver disease, renal 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 criterion15. History of laboratory-confirmed COVID-19 prior to enrolment (history of SARS-CoV-2 detection by PCR or antibody to SARS-CoV-2)16. Significant renal or hepatic impairment17. Scheduled elective surgery during the trial18. Life expectancy of <6 months19. Participation in another research trial involving an investigational product in the past 12 weeks20. Insufficient level of English language to undertake all study requirements in the opinion of the Investigators21. If at Visit 1 Screening & Vaccination the volunteer has either of the following, they will not be enrolled that day, however, they may be considered for enrolment later in the trial, if they recover in sufficient time: 21.1. Acute respiratory illness (moderate or severe illness with or without fever)21.2. Fever (oral temperature >37.8°C)

1. Receipt of any vaccine (licensed or investigational) other than the study intervention within 30 days before and after each study vaccination (one week for licensed seasonal influenza vaccine or pneumococcal vaccine)2. 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, any coronavirus vaccines)3. Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccines4. Any confirmed or suspected immunosuppressive or immunodeficient state, asplenia, recurrent severe infections, or use of immunosuppressant medication within the past 6 months, with the exception of topical steroids or short-term oral steroids (course lasting =14 days)5. History of 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)6. Any history of anaphylaxis 7. Pregnancy, lactation, or willingness/intention to become pregnant within 3 months post boost vaccine8. Current diagnosis of or treatment for cancer (with the exception of basal cell carcinoma of the skin and cervical carcinoma in situ) 9. Bleeding disorder (e.g. factor deficiency, coagulopathy, or platelet disorder), or prior history of significant bleeding or bruising following IM injections or venepuncture10. 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 dependency12. 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 data13. Severe and/or uncontrolled cardiovascular disease, respiratory disease, gastrointestinal disease, liver disease, renal 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 criterion15. History of laboratory-confirmed COVID-19 prior to enrolment (history of SARS-CoV-2 detection by PCR or antibody to SARS-CoV-2)16. Significant renal or hepatic impairment17. Scheduled elective surgery during the trial18. Life expectancy of <6 months19. Participation in another research trial involving an investigational product in the past 12 weeks20. Insufficient level of English language to undertake all study requirements in the opinion of the Investigators21. If at Visit 1 Screening & Vaccination the volunteer has either of the following, they will not be enrolled that day, however, they may be considered for enrolment later in the trial, if they recover in sufficient time: 21.1. Acute respiratory illness (moderate or severe illness with or without fever)21.2. Fever (oral temperature >37.8°C)

1. Receipt of any vaccine (licensed or investigational) other than the study intervention within 30 days before and after each study vaccination (one week for licensed seasonal influenza vaccine or pneumococcal vaccine) 2. 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, any coronavirus vaccines) 3. Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccines 4. Any confirmed or suspected immunosuppressive or immunodeficient state, asplenia, recurrent severe infections, or use of immunosuppressant medication within the past 6 months, with the exception of topical steroids or short-term oral steroids (course lasting =14 days) 5. History of 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) 6. Any history of anaphylaxis 7. Pregnancy, lactation, or willingness/intention to become pregnant within 3 months post boost vaccine 8. Current diagnosis of or treatment for cancer (with the exception of basal cell carcinoma of the skin and cervical carcinoma in situ) 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, 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 (history of SARS-CoV-2 detection by PCR or antibody to SARS-CoV-2) 16. Significant renal or hepatic impairment 17. Scheduled elective surgery during the trial 18. Life expectancy of <6 months 19. Participation 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 opinion of the Investigators 21. If at Visit 1 Screening & Vaccination the volunteer has either of the following, they will not be enrolled that day, however, they may be considered for enrolment later in the trial, if they recover in sufficient time: 21.1. Acute respiratory illness (m

1. Receipt of any vaccine (licensed or investigational) other than the study intervention within 30 days before and after each study vaccination (one week for licensed seasonal influenza vaccine or pneumococcal vaccine) 2. 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, any coronavirus vaccines) 3. Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccines 4. Any confirmed or suspected immunosuppressive or immunodeficient state, asplenia, recurrent severe infections, or use of immunosuppressant medication within the past 6 months, with the exception of topical steroids or short-term oral steroids (course lasting =14 days) 5. History of 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) 6. Any history of anaphylaxis 7. Pregnancy, lactation, or willingness/intention to become pregnant within 3 months post boost vaccine 8. Current diagnosis of or treatment for cancer (with the exception of basal cell carcinoma of the skin and cervical carcinoma in situ) 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, 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 (history of SARS-CoV-2 detection by PCR or antibody to SARS-CoV-2) 16. Significant renal or hepatic impairment 17. Scheduled elective surgery during the trial 18. Life expectancy of <6 months 19. Participation 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 opinion of the Investigators 21. If at Visit 1 Screening & Vaccination the volunteer has either of the following, they will not be enrolled that day, however, they may be considered for enrolment later in the trial, if they recover in sufficient time: 21.1. Acute respiratory illness (m