[{"arm_notes": "", "treatment_id": null, "treatment_name": "Study participants will be randomly allocated to receive one of the following at visit 1 at the same time as their second COVID-19 vaccine (either ChadOx1-nCOV-19 (AstraZeneca/Oxford) vaccine or BNT162b2 (Pfizer BioNTech) vaccine): 1. Investigational Medicinal Product (IMP): Influenza vaccine (Flucelvax QIV if the participant is aged <65 years or FluAd (MF59) if the participant is aged =65 years) 2. Placebo: Sodium chloride 0.9% injection Participants; laboratory staff; and clinicians assessing causality will be blinded to the treatment allocation. Randomisation will be performed using a secure internet-based randomisation system ensuring allocation concealment by a member of the local research team. Participants will be allocated in a 1:1 ratio to COVID-19 vaccine plus influenza vaccine or COVID-19 vaccine plus placebo vaccine. The allocation will be computer-generated and will be stratified by age (under 65 years; 65 years or over); type of vaccine (ChAdOx1 or BNT162b2); and centre by an independent BTC CTEU statistician; not involved in the trial; before recruitment begins. Approximately 3 weeks later participants will receive the other intervention (participants receiving the influenza vaccine at visit 1 will receive the placebo at visit 2; and participants receiving the placebo at visit 1 will receive the influenza vaccine at visit 2)", "treatment_type": "TODO", "pharmacological_treatment": "TODO"}, {"arm_notes": "", "treatment_id": null, "treatment_name": "1. Investigational Medicinal Product (IMP): Influenza vaccine (Flucelvax QIV if the participant is aged <65 years or FluAd (MF59) if the participant is aged =65 years)", "treatment_type": "TODO", "pharmacological_treatment": "TODO"}, {"arm_notes": "", "treatment_id": null, "treatment_name": "2. Placebo: Sodium chloride 0.9% injection", "treatment_type": "Placebo", "pharmacological_treatment": "TODO"}]

[{"arm_notes": "Previously received one COVID-19 vaccine dose 56 to 90 days prior enrolment;1+1", "treatment_id": 1446, "treatment_name": "Chadox1 ncov-19+flu vaccine", "treatment_type": "Non replicating viral vector+non covid vaccine", "pharmacological_treatment": "Vaccine+non covid vaccine"}, {"arm_notes": "Previously received one COVID-19 vaccine dose 56 to 90 days prior enrolment;1+1", "treatment_id": 1430, "treatment_name": "Bnt162b2+flu vaccine", "treatment_type": "Rna based vaccine+non covid vaccine", "pharmacological_treatment": "Vaccine+non covid vaccine"}, {"arm_notes": "", "treatment_id": 2187, "treatment_name": "Placebo", "treatment_type": "Placebo", "pharmacological_treatment": "Placebo"}]