Current exclusion criteria as of 27/08/2021: 1. Aged <16 years 2. Pregnancy 3. Use of active cancer treatment 4. Use of biological treatment 5. Previously confirmed COVID-19 6. Any organ transplantation 7. Single person household 8. Requires hospitalisation prior to study start 9. Required to take regular medications administered by inhalation, or via the naso- and oropharyngeal route 10. Asthma 11. Known allergies to BioBlock components Previous exclusion criteria: 1. Aged <16 years 2. Pregnancy 3. Use of active cancer treatment 4. Use of biological treatment 5. Previously vaccinated against COVID-19 6. Previously confirmed COVID-19 7. Any organ transplantation 8. Single person household 9. Requires hospitalisation prior to study start 10. Required to take regular medications administered by inhalation, or via the naso- and oropharyngeal route 11. Asthma 12. Known allergies to BioBlock components

Current exclusion criteria as of 27/08/2021: 1. Aged <16 years 2. Pregnancy 3. Use of active cancer treatment 4. Use of biological treatment 5. Previously confirmed COVID-19 6. Any organ transplantation 7. Single person household 8. Requires hospitalisation prior to study start 9. Required to take regular medications administered by inhalation, or via the naso- and oropharyngeal route 10. Asthma 11. Known allergies to BioBlock components Previous exclusion criteria: 1. Aged <16 years 2. Pregnancy 3. Use of active cancer treatment 4. Use of biological treatment 5. Previously vaccinated against COVID-19 6. Previously confirmed COVID-19 7. Any organ transplantation 8. Single person household 9. Requires hospitalisation prior to study start 10. Required to take regular medications administered by inhalation, or via the naso- and oropharyngeal route 11. Asthma 12. Known allergies to BioBlock components

1. Aged <16 years 2. Pregnancy 3. Use of active cancer treatment 4. Use of biological treatment 5. Previously vaccinated against COVID-19 6. Previously confirmed COVID-19 7. Any organ transplantation 8. Single person household 9. Requires hospitalisation prior to study start 10. Required to take regular medications administered by inhalation, or via the naso- and oropharyngeal route 11. Asthma 12. Known allergies to BioBlock components

1. Aged <16 years 2. Pregnancy 3. Use of active cancer treatment 4. Use of biological treatment 5. Previously vaccinated against COVID-19 6. Previously confirmed COVID-19 7. Any organ transplantation 8. Single person household 9. Requires hospitalisation prior to study start 10. Required to take regular medications administered by inhalation, or via the naso- and oropharyngeal route 11. Asthma 12. Known allergies to BioBlock components