Subjects can be included in the study if they have received three doses of a COVID-19 vaccine. The first two COVID-19 vaccines can be any combination of Comirnaty® (Pfizer-BioNTech), Spikevax (Moderna Inc), and Vaxzevria (AstraZeneca) but participants must have received a third dose of either Comirnaty® (Pfizer-BioNTech) or Spikevax (Moderna Inc) (not Vaxzevria (AstraZeneca). The third dose must have be administered at least four months prior to the commencement of the study (Day 0). Addition inclusion criteria are: 1. Participants must be healthy with no clinically significant underlying chronic conditions/illness 2. Aged 18–50 years (inclusive) at Day 0 (pre-dose), 3. With a body mass index (BMI) within the range 18.0–32.0 kg/m² (inclusive), 4. Satisfactory medical assessment: no clinically significant or relevant abnormalities (in the opinion of the Investigator) in medical history, physical examination, vital signs (blood pressure, tympanic temperature, heart rate, respiratory rate, ECG) and laboratory evaluation (haematology or biochemistry),

Subjects can be included in the study if they have received three doses of a COVID-19 vaccine. The first two COVID-19 vaccines can be any combination of Comirnaty® (Pfizer-BioNTech), Spikevax (Moderna Inc), and Vaxzevria (AstraZeneca) but participants must have received a third dose of either Comirnaty® (Pfizer-BioNTech) or Spikevax (Moderna Inc) (not Vaxzevria (AstraZeneca). The third dose must have be administered at least four months prior to the commencement of the study (Day 0). Addition inclusion criteria are: 1. Participants must be healthy with no clinically significant underlying chronic conditions/illness 2. Aged 18–50 years (inclusive) at Day 0 (pre-dose), 3. With a body mass index (BMI) within the range 18.0–32.0 kg/m² (inclusive), 4. Satisfactory medical assessment: no clinically significant or relevant abnormalities (in the opinion of the Investigator) in medical history, physical examination, vital signs (blood pressure, tympanic temperature, heart rate, respiratory rate, ECG) and laboratory evaluation (haematology or biochemistry),