Effectiveness of the first and the second dose of COVID-19 vaccines in Serbia during the first three months of rollout

Introduction/Objective. The main aim of this study was to assess COVID-19 vaccination effectiveness (VE) of BBIBP-CorV, Gam-COVID-Vac, BNT162b2, and ChAdOx1-nCoV-19 in Serbia during the first three months of rollout. Methods. The data from the Serbian National Immunization Registry, the Primary Health Centre Report and the University Clinical Centre Report for Kragujevac, Serbia, for the period from Jan 1st to March 31st 2021 were used to compare COVID-19 vaccinated population to unvaccinated individuals in terms of laboratory confirmed SARS-CoV-2 infection, COVID-19-related hospitalization and intensive care unit (ICU) admission due to COVID-19. VE was estimated based on the incidence rate ratio, adjusted for age and sex. Results. Overall VE after the first dose reached 20.6%, 28.2% and 56.1%, and 55.7%, 63.9% and 79.8% after second dose for SARS-CoV-2 infection, COVID-19-related hospitalization and ICU admission, respectively. BNT162b2 exhibited 96.7% VE against infection and no hospitalization after second dose. Complete vaccination with BBIBP-CorV and Gam-COVID-Vac demonstrated VE of 43.2% and 78.6% against infection, 56.9% and 85.3% against hospitalization, and 82.3% and 52.7% against ICU admission, respectively. ChAdOx1-nCoV-19 after the first received dose showed VE of 10.3% and 74.7% against infection and hospitalization, with no ICU admission. Conclusion. COVID-19 vaccination in general, as well as each of the four studied vaccines, reduces the risk of SARS-CoV-2 infection, hospitalization due to COVID-19, and COVID-19-related ICU admission. Vaccine effectiveness significantly increases with the second received dose for all study outcomes.