Inclusion criteria:  Age ≥ 16 years  For asthma patients:  Diagnosis of severe asthma (based on ATS/ERS consensus criteria) Group A: Currently receiving an asthma biologic with treatment having started at least 3 months before first COVID-19 vaccine Group B: on maintenance oral steroids at a dose of ≥5mg prednisolone (or equivalent) per day (at the time of first COVID-19 vaccine) Group C: not on asthma biologic or maintenance oral steroids (at the time of vaccination) or stopped ≥3 months prior to first COVID-19 vaccine  Exclusion criteria:  Current pregnancy or planning a pregnancy within the next 6 months Current malignancy Diagnosis of immunodeficiency requiring treatment  Additional exclusion criteria for asthma patients:  Group A: maintenance oral steroids at the time of first COVID-19 vaccine Group B: on an asthma biologic at the time of first COVID-19 vaccine  Additional exclusion criteria for healthy controls cohort (as assessed by research team):  No history of asthma or significant other lung disease Severe chronic inflammatory disease Severe cardiac disease Diabetes Previous proven COVID-19 infection Inability to provide informed consent Unwilling to have vaccination Participation in another clinical trial involving an investigational medicinal product (IMP).