inclusion criteria: * over 18 years of age * healthcare worker * this is defined as anyone who works in a healthcare setting or has face to face contact with patients. * provide a signed and dated informed consent form * australian sites only: if annual influenza vaccination is available, receiving the flu vaccine is an eligibility requirement. the flu vaccine will be required a minimum of 3 days in advance of randomisation in the brace trial. * pre-randomisation blood collected

inclusion criteria: * over 18 years of age * healthcare worker * this is defined as anyone who works in a healthcare setting or has face to face contact with patients. * provide a signed and dated informed consent form * australian sites only: if annual influenza vaccination is available, receiving the flu vaccine is an eligibility requirement. the flu vaccine will be required a minimum of 3 days in advance of randomisation in the brace trial. * pre-randomisation blood collected

inclusion criteria: - over 18 years of age - healthcare worker - this is defined as anyone who works in a healthcare setting or has face to face contact with patients. - provide a signed and dated informed consent form - australian sites only: if annual influenza vaccination is available, receiving the flu vaccine is an eligibility requirement. the flu vaccine will be required a minimum of 3 days in advance of randomisation in the brace trial. - pre-randomisation blood collected

inclusion criteria: - over 18 years of age - healthcare worker - this is defined as anyone who works in a healthcare setting or has face to face contact with patients. - provide a signed and dated informed consent form - australian sites only: if annual influenza vaccination is available, receiving the flu vaccine is an eligibility requirement. the flu vaccine will be required a minimum of 3 days in advance of randomisation in the brace trial. - pre-randomisation blood collected

inclusion criteria: - over 18 years of age - healthcare worker - this is defined as anyone who works in a healthcare setting or has face to face contact with patients. - provide a signed and dated informed consent form - if annual influenza vaccination is available, receiving the flu vaccine is an eligibility requirement. the flu vaccine will be required a minimum of 3 days in advance of - pre-randomisation blood collected

inclusion criteria: - over 18 years of age - healthcare worker - this is defined as anyone who works in a healthcare setting or has face to face contact with patients. - provide a signed and dated informed consent form - if annual influenza vaccination is available, receiving the flu vaccine is an eligibility requirement. the flu vaccine will be required a minimum of 3 days in advance of - pre-randomisation blood collected