Current participant inclusion criteria as of 10/01/2022: 1. Willing and able to give written informed consent for participation in the trial. 2. Aged 30 years or above and in good health as determined by a trial clinician. Participants may have well controlled or mild-moderate comorbidity. 3. Female participants of childbearing potential must be willing to ensure that they or their partner use effective contraception from 1 month prior to first immunisation continuously until 3 months after boost immunisation 4. In the Investigator’s opinion, is able and willing to comply with all trial requirements. 5. Willing to allow their General Practitioner and consultant, if appropriate, to be notified of participation in the trial 6. Willing to allow investigators to discuss the volunteer’s medical history with their General Practitioner and access all medical records when relevant to study procedures. 7. Agreement to refrain from blood donation during the study 8. Received priming dose of COVID-19 vaccination between December 2020 and January 2021 (inclusive) and booster dose no less than 84 days prior to day 0. Due to the NHS deployment timelines, some sites may need to invite people who have been prime-boosted with their second dose of AstraZeneca with a minimum of 70 days from their second dose. Sites need Sponsor approval for this prior to enrolment of people with a 70-83 day gap since their second dose in any study arm For the External Vaccine Trial Participants sub-study, the inclusion criteria are: 1. Willing and able to give written informed consent for participation in the trial 2. Male or female aged 30 years or above 3. In the Investigator’s opinion, is able and willing to comply with all trial requirements 4. Willing to allow their General Practitioner and consultant, if appropriate, to be notified of participation in the trial 5. Willing to allow investigators to discuss the volunteer’s medical history with their General Practitioner and access all medical records when relevant to study procedures 6. Primary immunization course (2 doses) of NVXCoV2373 COVID-19 vaccine 7. Plans to receive 1 or 2 doses of licensed vaccine (1 dose will be received as part of this trial, the second dose will not be provided by the trial but the participant may receive a second dose via the NHS if they wish to). Previous participant inclusion criteria: 1. Willing and able to give written informed consent for participation in the trial. 2. Aged 30 years or above and in good health as determined by a trial clinician. Participants may have well controlled or mild-moderate comorbidity. 3. Female participants of childbearing potential must be willing to ensure that they or their partner use effective contraception from 1 month prior to first immunisation continuously until 3 months after boost immunisation 4. In the Investigator’s opinion, is able and willing to comply with all trial requirements. 5. Willing to allow their General Practitioner and consultant, if appropriate, to be notified of participation in the trial 6. Willing to allow investigators to discuss the volunteer’

Current participant inclusion criteria as of 10/01/2022: 1. Willing and able to give written informed consent for participation in the trial. 2. Aged 30 years or above and in good health as determined by a trial clinician. Participants may have well controlled or mild-moderate comorbidity. 3. Female participants of childbearing potential must be willing to ensure that they or their partner use effective contraception from 1 month prior to first immunisation continuously until 3 months after boost immunisation 4. In the Investigator’s opinion, is able and willing to comply with all trial requirements. 5. Willing to allow their General Practitioner and consultant, if appropriate, to be notified of participation in the trial 6. Willing to allow investigators to discuss the volunteer’s medical history with their General Practitioner and access all medical records when relevant to study procedures. 7. Agreement to refrain from blood donation during the study 8. Received priming dose of COVID-19 vaccination between December 2020 and January 2021 (inclusive) and booster dose no less than 84 days prior to day 0. Due to the NHS deployment timelines, some sites may need to invite people who have been prime-boosted with their second dose of AstraZeneca with a minimum of 70 days from their second dose. Sites need Sponsor approval for this prior to enrolment of people with a 70-83 day gap since their second dose in any study arm For the External Vaccine Trial Participants sub-study, the inclusion criteria are: 1. Willing and able to give written informed consent for participation in the trial 2. Male or female aged 30 years or above 3. In the Investigator’s opinion, is able and willing to comply with all trial requirements 4. Willing to allow their General Practitioner and consultant, if appropriate, to be notified of participation in the trial 5. Willing to allow investigators to discuss the volunteer’s medical history with their General Practitioner and access all medical records when relevant to study procedures 6. Primary immunization course (2 doses) of NVXCoV2373 COVID-19 vaccine 7. Plans to receive 1 or 2 doses of licensed vaccine (1 dose will be received as part of this trial, the second dose will not be provided by the trial but the participant may receive a second dose via the NHS if they wish to). Previous participant inclusion criteria: 1. Willing and able to give written informed consent for participation in the trial. 2. Aged 30 years or above and in good health as determined by a trial clinician. Participants may have well controlled or mild-moderate comorbidity. 3. Female participants of childbearing potential must be willing to ensure that they or their partner use effective contraception from 1 month prior to first immunisation continuously until 3 months after boost immunisation 4. In the Investigator’s opinion, is able and willing to comply with all trial requirements. 5. Willing to allow their General Practitioner and consultant, if appropriate, to be notified of participation in the trial 6. Willing to allow investigators to discuss the volunteer’

1. Willing and able to give written informed consent for participation in the trial. 2. Aged 30 years or above and in good health as determined by a trial clinician. Participants may have well controlled or mild-moderate comorbidity. 3. Female participants of childbearing potential must be willing to ensure that they or their partner use effective contraception from 1 month prior to first immunisation continuously until 3 months after boost immunisation 4. In the Investigator’s opinion, is able and willing to comply with all trial requirements. 5. Willing to allow their General Practitioner and consultant, if appropriate, to be notified of participation in the trial 6. Willing to allow investigators to discuss the volunteer’s medical history with their General Practitioner and access all medical records when relevant to study procedures. 7. Agreement to refrain from blood donation during the study 8. Received priming dose of COVID-19 vaccination between December 2020 and January 2021 (inclusive) and booster dose no less than 84 days prior to day 0

1. Willing and able to give written informed consent for participation in the trial. 2. Aged 30 years or above and in good health as determined by a trial clinician. Participants may have well controlled or mild-moderate comorbidity. 3. Female participants of childbearing potential must be willing to ensure that they or their partner use effective contraception from 1 month prior to first immunisation continuously until 3 months after boost immunisation 4. In the Investigator’s opinion, is able and willing to comply with all trial requirements. 5. Willing to allow their General Practitioner and consultant, if appropriate, to be notified of participation in the trial 6. Willing to allow investigators to discuss the volunteer’s medical history with their General Practitioner and access all medical records when relevant to study procedures. 7. Agreement to refrain from blood donation during the study 8. Received priming dose of COVID-19 vaccination between December 2020 and January 2021 (inclusive) and booster dose no less than 84 days prior to day 0