This will be a randomized single-blind controlled trial to determine the immunogenicity, efficacy and safety of IH Convidecia (CanSino), as a second booster vaccination against Omicron and other emerging VOCs to prevent breakthrough infections among people with a sub-optimal immune response to the first booster dose.

These subjects will be randomized in a ratio of 1:1 to receive a second booster dose of IH Convidecia vaccine (treatment arm), or a second booster dose of mRNA vaccine BNT162b2 (Pfizer).

Inclusion Criteria:

• Participant is willing and able to give written informed consent for participation in the study.
• Male or Female, aged 18 years or above and in good health as determined by study clinician. Participants may have well controlled or mild-moderate comorbidity.
• 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.
• In the Investigator's opinion, participant is able and willing to comply with all trial requirements.
• At least 16 weeks after first booster dose of vaccination.

Exclusion Criteria:

• Confirmed cases, suspected cases or asymptomatic cases of COVID-19.
• Self-reported history of SARS and MERS infection.
• Receipt of live attenuated vaccine within one month prior to vaccination and other vaccines within 14 days prior to vaccination.
• Receipt of any SARS-COV-2 vaccine after first dose of booster vaccination.
• Participants who are pregnant at enrolment or planning to become pregnant during the first 3 months following vaccination.
• Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccines.
• History of allergic disease or reactions likely to be exacerbated by any component of study vaccines.
• Any history of anaphylaxis.
• Bleeding disorder (e.g. factor deficiency, coagulopathy or platelet disorder), or continuous use of anticoagulants (warfarin, apixaban, rivaroxaban, dabigatran, edoxaban), or prior history of significant bleeding or bruising following IM injections or venipuncture.
• Suspected or known current alcohol or drug dependency.
• 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.
• 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).
• Participant with life expectancy of less than 6 months.

Observer-blind clinical trial