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.