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Effectiveness of vaccination in preventing severe SARS CoV-2 infection in South India-a hospital based cross sectional study

Background & objectives: Establishing concrete evidence on effect of vaccination on severity of SARS CoV-2 infections in real world situations is the need of the hour. The aim of this study is to estimate the effectiveness Covid 19 vaccines in preventing the new and severe SARS CoV-2 infections. Methods: We did this retrospective cross-sectional study among the 4765 patients consecutive adult inpatients admitted in the Covid 19 wards of a tertiary care hospital from May 1,2021 to July 7, 2021 during the second wave of Covid 19 pandemic. Information on basic demographic variables, RT PCR status, vaccination status, outcome and clinical severity of illness were obtained from the electronic hospital patient records. Results, and Interpretation & conclusions: Type of vaccine and number of doses of vaccines didnot have any protective effect against new SARS CoV-2 infection. Covid 19 patients vaccinated with at least one dose had 75 % less risk of requiring oxygen (OR 0.25 CI: 0.15 to 0.44) and 60 % less risk of ICU admission (OR 0.4 CI: 0.2 to 0.6) and it was statistically significant. Only 31 % of fully vaccinated Covid 19 positive patients had oxygen requirement (90% less risk) and 15% of the fully vaccinated patients had needed ICU admission (90% less risk). Conclusion: Vaccination didnot protect against SARS Cov-2 infection however significant protection was documented against severe SARS Cov-2 infection. Vaccination coverage should be increased urgently in order to halt the impending wave of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.