Various vaccines for protection against COVID-19 were provided emergency approval in late 2020 to early 2021. Despite more than 1.5 years of public use, no long-term safety data has been released by any vaccine manufacturer. The main aim of this study is to provide the one-year safety results of the ChAdOx1-nCoV-19/AZD1222 vaccine. Risk factors of development of adverse events of special interest (AESIs) as well as persistent AESIs have been determined. Methodology: This was a prospective

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... ational study conducted from February 2021 to April 2022 in a tertiary hospital of North India and its two associated centers. Health care workers, other frontline workers, and the elderly vaccinated with the ChAdOx1-nCoV-19 corona virus vaccine constituted the study population. Individuals were contacted telephonically at pre-decided intervals for one year and health issues of significant concern were recorded. Regression analysis was conducted to determine risk factors of AESI occurrence and determinants of persistent AESIs. Results: Of 1650 individuals enrolled, 1520 could be assessed for outcomes of interest. COVID-19 at any time post vaccination occurred in 44.1% participants. Dengue occurred in 8% participants and was of 'serious' category (FDA) in 19.7% of those affected. Majority of the AESIs belonged to the MedDRA system organ class (SOC) of musculoskeletal disorders (3.7%) followed by general disorders and administration site conditions (2.1%) and infections (2%). Arthropathy in the form of knee joint involvement was the commonest individual AESI (1.7%). New onset hypertension, thyroid function abnormalities and diabetes occurred respectively in 0.9%, 0.4% and 0.3% participants. Five deaths and eleven 'serious' adverse events were reported. Among participants receiving booster dose of the COVID-19 vaccine (n=184), 9.8% developed adverse events of concern, of which urticaria and new onset arthropathy were common. Regression analysis showed females, individuals with pre-vaccination history of COVID-19, diabetes, hypothyroidism and arthropathy had a 1.78-, 1.55-, 1.82-, 2.47-and 3.9-times higher odds of AESI development. Females and individuals with hypothyroidism were also at 1.66-and 2.23-times higher risk of persistent AESIs. Receiving any dose Qeios, CC-BY 4.0 • Article,