Inclusion Criteria:  Participant is willing to give written informed consent for participation in the trial. Participants should receive 2 doses of the AZD1222. Evidence of this will be gathered from medical history and/or medical records including the COVID-19 vaccine registration yellow card.  Exclusion Criteria:  The participant may not enter the trial if ANY of the following apply:  Fever or evidence of upper respiratory tract infections Confirmed COVID-19 cases (PCR-confirmed infection or detectable anti-nucleocapsid protein IgG) History of anaphylaxis, severe 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 listed ingredients of any study vaccine). Malignancy requiring receipt of immunosuppressive chemotherapy or radiotherapy for treatment of solid organ cancer/hematological malignancy within the 6 months prior to enrollment. Bleeding disorder (e.g. factor deficiency, coagulopathy or platelet disorder), or prior history of significant bleeding or bruising following intramuscular injections or venipuncture. Has received vaccines other than COVID-19 vaccine within one month Pregnancy or willingness/intention to become pregnant within 3 months post booster vaccine Aged < 20 years or unable to sign the informed consent 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 or insufficient level of language to undertake all study requirements in the opinion of the Investigators.