INTRODUCTION:
COVID-19 vaccination has been shown to be a critical intervention to
reduce morbidity and mortality from COVID-19. Protecting health workers
(HCWs) through COVID-19 immunization is essential for effective control
of the COVID-19 pandemic; HCWs are highly exposed to infection, have
frequent contact with vulnerable patients, and are essential to the
ongoing function of health services.
While many observational studies have evaluated the effectiveness of
mRNA and viral vector vaccines, much less is known about the real-world
effectiveness of whole inactivated virus vaccines. Inactivated
whole-virus vaccines, which have potential advantages of being easier to
produce and store, and also presenting a wider range of viral antigens
to the immune system, accounted for nearly half of the 7.3 billion
COVID-19 vaccine doses delivered globally, as of October 2021. Most of
these doses have been used in low- and middle-income countries (LMICs),
where few studies have evaluated the effectiveness of COVID-19 vaccines
in general. In LMICs, differences in population demographics and
differences in operational aspects of the vaccination campaign could
potentially impact real-world vaccine effectiveness (VE).
CoronaVac (Sinovac, Beijing), a newly-developed inactivated vaccine
authorized for emergency use by WHO in June 2021, has been widely used
in countries in Central Asia and other countries in the eastern part of
the European Region of the World Health Organization (WHO); however only
one study from the region – a study of HCWs in Turkey conducted during
a period of alpha variant predominance – has evaluated the
effectiveness of this vaccine.
In Azerbaijan, an upper-middle income country in the European region of
WHO with a population of approximately 10 million people, the COVID-19
vaccination campaign began on January 18, 2021. Populations considered
most at risk, including HCWs, were prioritized for early vaccination.
CoronaVac was the main vaccine available at the beginning of the
vaccination campaign.
We conducted a prospective cohort study of COVID -19 vaccine
effectiveness in HCWs in Azerbaijan. In this interim analysis of the
study, we aimed to estimate the early VE of primary series (two-dose)
CoronaVac against PCR-confirmed SARS-CoV-2 illness during
March-November, 2021.