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.