ARM 2 1. Previous diagnosis of COVID-19 (microbiologically proven, either symptomatic or asymptomatic) 2. Any contra-indication to intra-nasal IFN-a such as severe nasal bleeding requiring intervention, nasal malignancy, nasal deformity, radiotherapy to the nasopharynx and/or oropharynx 3. Pregnant or breast-feeding women, or women who wish to become pregnant during the course of the study 4. Patient unable to return for follow-up 5. Life expectancy of less than 1 month 6. Patient already included in another intervention study on the prevention of COVID-19 7. Currently unwell with influenza-like symptoms

ARM 2 1. Previous diagnosis of COVID-19 (microbiologically proven, either symptomatic or asymptomatic) 2. Any contra-indication to intra-nasal IFN-a such as severe nasal bleeding requiring intervention, nasal malignancy, nasal deformity, radiotherapy to the nasopharynx and/or oropharynx 3. Pregnant or breast-feeding women, or women who wish to become pregnant during the course of the study 4. Patient unable to return for follow-up 5. Life expectancy of less than 1 month 6. Patient already included in another intervention study on the prevention of COVID-19 7. Currently unwell with influenza-like symptoms