inclusion criteria: * age ≥18 years; * study participants who have given informed consent, and received a copy of signed consent form prior to any study related procedures; * healthcare professionals (nurses, doctors, allied health professionals, health care assistants, operating department practitioners) working in swansea bay university health board initially as well as any other volunteers \>18 years who have not previously tested positive for covid19 or been vaccinated. * subjects agree to refrain from taking over the counter products intended to prevent, intervene in, or treat colds/flu, starting at study entry and continuing through week 10 of the study.

inclusion criteria: * age ≥18 years; * study participants who have given informed consent, and received a copy of signed consent form prior to any study related procedures; * healthcare professionals (nurses, doctors, allied health professionals, health care assistants, operating department practitioners) working in swansea bay university health board initially as well as any other volunteers \>18 years who have not previously tested positive for covid19 or been vaccinated. * subjects agree to refrain from taking over the counter products intended to prevent, intervene in, or treat colds/flu, starting at study entry and continuing through week 10 of the study.

inclusion criteria: - age ≥18 years; - study participants who have given informed consent, and received a copy of signed consent form prior to any study related procedures; - healthcare professionals (nurses, doctors, allied health professionals, health care assistants, operating department practitioners) working in swansea bay university health board initially as well as any other volunteers >18 years who have not previously tested positive for covid19 or been vaccinated. - subjects agree to refrain from taking over the counter products intended to prevent, intervene in, or treat colds/flu, starting at study entry and continuing through week 10 of the study.

inclusion criteria: - age ≥18 years; - study participants who have given informed consent, and received a copy of signed consent form prior to any study related procedures; - healthcare professionals (nurses, doctors, allied health professionals, health care assistants, operating department practitioners) working in swansea bay university health board initially as well as any other volunteers >18 years who have not previously tested positive for covid19 or been vaccinated. - subjects agree to refrain from taking over the counter products intended to prevent, intervene in, or treat colds/flu, starting at study entry and continuing through week 10 of the study.

inclusion criteria: - age ≥18 years; - study participants who have given informed consent, and received a copy of signed consent form prior to any study related procedures; - healthcare professionals (nurses, doctors, allied health professionals, health care assistants, operating department practitioners) working in swansea bay university health board; - subjects agree to refrain from taking over the counter products intended to prevent, intervene in, or treat colds/flu, starting at study entry and continuing through week 8 of the study. medications in table 2 (section 4.3) are specifically disallowed.

inclusion criteria: - age ≥18 years; - study participants who have given informed consent, and received a copy of signed consent form prior to any study related procedures; - healthcare professionals (nurses, doctors, allied health professionals, health care assistants, operating department practitioners) working in swansea bay university health board; - subjects agree to refrain from taking over the counter products intended to prevent, intervene in, or treat colds/flu, starting at study entry and continuing through week 8 of the study. medications in table 2 (section 4.3) are specifically disallowed.