Clinical Research Directory

Inclusion Criteria: * Aged 30 years or older at enrolment. * Have received two doses of any inactivated COVID-19 vaccines (for example Sinovac- CoronaVac, Sinopharm-BIBP) with the most recent dose at least 90 days prior to enrolment. * Currently resident and planning to remain resident in Hong Kong during the duration of the study, i.e. for 12 months after enrolment. * Agreement to refrain from blood donation during the course of the study. * Willing to provide blood samples for all the required time points. * The individual or their caregiver have a home phone or cellular or mobile phone for communications purpose. * Capable of providing informed consent. Exclusion Criteria: * A history of laboratory-confirmed or clinically confirmed COVID-19 infection. Have received (at least one dose of) any COVID-19 vaccines other than inactivated vaccines. * Individuals who report any medical condition, or as determined by a clinician, not suitable to receive mRNA vaccines, including but not limited to allergies to the active substance or other ingredients of the vaccine. * With diagnosed medical conditions related to their immune system. * Use of medication that impairs immune system in the last 6 months, except topical steroids or short-term oral steroids (course lasting ≤ 14 days). * Have used immunoglobulins and/or any blood products within 90 days prior to enrolment (administration of the study vaccine). * Pregnancy, lactation or intention to become pregnant in the coming 3 months.