Effectiveness of Vaccination in Preventing Coronavirus Disease 2019 Six Months or More After the Second Dose and Up to Five Months After the Third Dose in The Municipality of Voždovac (Belgrade, Serbia): A Real-Life Comparison of Four Vaccines

Background: Availability of vaccines less than a year after the beginning of the coronavirus disease 2019 (COVID-19) pandemic, followed by the widest vaccination campaign in history, significantly altered the global course of the pandemic.Data on Vaccine Effectiveness (VE) are important for immunization policies, as well as vaccine acceptance, especially among populations susceptible to severe infection.Aims: To assess the relative risk of COVID-19 in the vaccinated vs. unvaccinated population and compare the effectiveness of four vaccines (BBIBP-CorV, BNT162b2, Gam-COVID-Vac, ChAdOx1) against symptomatic infection.Study Design: Retrospective, cross-sectional observational study.Methods: We examined the incidence of SARS-CoV-2 infection and clinically overt COVID-19 in a five-month period (November 1 st , 2021 -March 31 st , 2022) in the Belgrade municipality of Vodovac.The observed period corresponded to the predominance of Delta and Omicron variants.Data on vaccinal status were retrieved from the National Registry for Immunization against COVID-19 at the Institute for Public Health of Serbia, while information on vaccine type was obtained by telephone interview in people with polymerase chain reaction (PCR)-confirmed infection.Only those who received two or three vaccine doses were included in the study.Results: Of the total population of Vodovac (169,567), 88,870 people (52.4%) were vaccinated with two or three doses by the end of the study