To be eligible a person must: 1. Be equal to or over 18 years of age. 2. Have received two doses of Pfizer Comirnaty (Pf) or two doses of COVID-19 Vaccine Astra Zeneca (AZ). 3. Be eligible and willing to receive a COVID-19 booster vaccine authorised for use (including emergency use authorisation) by the TGA or equivalent regulatory authority. 4. Be registered on the Australian Immunisation Register (AIR), or otherwise possess evidence of primary vaccination. 5. Be willing to comply with trial requirements, including the provision of blood and saliva samples at the indicated time intervals.

To be eligible a person must: 1. Be equal to or over 18 years of age. 2. Have received two doses of Pfizer Comirnaty (Pf) or two doses of COVID-19 Vaccine Astra Zeneca (AZ). 3. Be eligible and willing to receive a COVID-19 booster vaccine authorised for use (including emergency use authorisation) by the TGA or equivalent regulatory authority. 4. Be registered on the Australian Immunisation Register (AIR), or otherwise possess evidence of primary vaccination. 5. Be willing to comply with trial requirements, including the provision of blood and saliva samples at the indicated time intervals.