Study setting and population
The study design and analysis were guided by the WHO European Region HCW VE guidance document, and the study was conducted within the framework of WHO’s Unity platform.
From May 3 to July 17, 2021, we enrolled HCWs at seven hospitals in the Baku United Hospital network in Baku, the capital city of Azerbaijan, into a prospective cohort. We selected hospitals based on accessibility by the study team in the context of quarantine-related restrictions to travel at the time. At the time of enrolment and during the study period, all sites admitted patients with COVID-19.
We offered enrolment to all HCWs employed by participating hospitals for whom COVID-19 vaccination was not contra-indicated by previous allergy to vaccinations. National guidance at the time required HCWs to wait 6 months from PCR-confirmed infection before receiving the first dose. The national vaccination schedule recommended administration of the second dose of CoronaVac 14-21 days after the first.
Lists of all HCWs employed at study sites were provided by hospital directors to guide recruitment. We invited all HCWs to participate, including physicians, nurses, clinical support staff, and custodial workers, regardless of their COVID-19 vaccination status, intention to get vaccinated in future, or history of previous infection with SARS-CoV-2. At the time of enrolment, and throughout the analysis period, HCWs were required to have COVID-19 vaccination in order to work in hospitals in Azerbaijan; however, because of limited availability of the vaccine in much of the first half of 2021, this requirement was not strictly enforced.