Vaccine effectiveness to protect against moderate or severe disease in COVID cases: A prospective cohort study.

Background: This study was carried out to evaluate the effectiveness of partial and full vaccination with ChAdOx1 nCoV-19 (COVISHIELD) to prevent the development of moderate or severe illness among COVID-positive cases.

Methods: This prospective cohort study was conducted among Armed Forces personnel deployed in Northern India who were found COVID positive during the study period between January and June 2021. Information about the vaccination status, age and comorbidities was collected at the time of diagnosis.