A new wave of COVID-19 infections, mainly caused by the Omicron/ Delta variant, has been sweeping the globe since the start of 2022. In response, the administration of a third dose of COVID-19 vaccine was considered to address potential waning immunity over time and reduced effectiveness against the Omicron/ Delta variant. The pandemic also resulted in many infections among health care workers (HCWs) and their households. In this study, a retrospective analysis would perform on risk of COVID-19 infection and their outcome in relation to their COVID-19 vaccination history by using the data repository from one of the Hong Kong private hospitals.

HCWs were required to submit a standardized online self-declaration form for report of 1) demographic of the HCWs, 2) symptoms related history and 3) COVID-19 exposure history once they were COVID-19 confirmed by rapid antigen test against COVID-19 and/or polymerase chain reaction (PCR) test for COVID-19. Subsequent follow up such as contact tracing, COVID-19 PCR testing results of these HCWs and status of return to work were captured by the infection control team in a systematic manner.

Inclusion Criteria:

• All full time staff members of the private hospital

Exclusion Criteria:

• History of COVID-19 before 2022

All full time staff members of the private hospital