1. Healthy males and non-pregnant females 2. Aged 18 - 50 years 3. Immunised no less than 12 weeks prior with 2 doses of SARS-CoV-2 vaccine 4. No history of serological evidence of prior SARS-CoV-2 infection (seronegative for N)

1. Healthy males and non-pregnant females 2. Aged 18 - 50 years 3. Immunised no less than 12 weeks prior with 2 doses of SARS-CoV-2 vaccine 4. No history of serological evidence of prior SARS-CoV-2 infection (seronegative for N)