Impact of prior vaccination with Covishield™ and Covaxin® on mortality among symptomatic COVID-19 patients during the second wave of the pandemic in South India during April and May 2021: a cohort study

Background: COVID-19 vaccines were authorised for emergency use to mitigate the impact of the pandemic. This study evaluated the effect of prior vaccination with either Oxford Astra Zeneca's Covishield (TM) or Bharath Biotech's Covaxin (R) on mortality among symptomatic COVID-19 patients during the second wave of the pandemic in India. Methodology: In this cohort study comprising of RT-PCR confirmed symptomatic COVID-19 patients presenting during April and May 2021, the effect of prior vaccination on mortality (primary outcome), need for hospitalization, oxygen therapy, non-invasive ventilation (NIV) and intensive care unit (ICU) admission were assessed and expressed as risk ratio (RR) with 95% confidence intervals (CI). Results: The mean (SD) age of the cohort (n = 4183) was 46.3 (15.5) years; 17.9% (748/4183) had received at least one dose of CovishieldTM and 4.8% (201/4183) had received Covaxin (R). Mortality was 0.2% (95% CI: 0.2% - 0.7%), 3.5% (1.9-5.2%), 6.2% (0.3-12%) and 12.9% (11.8-14.1%) among fully vaccinated (>2 weeks after two doses), partially vaccinated (>2 weeks after one dose or <2 weeks after two doses), indeterminate (<2 weeks after one dose) and unvaccinated patients respectively. The difference in mortality among unvaccinated vs. fully vaccinated was 12.7% (95% CI: 11.4-13.9%), unvaccinated vs. partially vaccinated was 9.4% (7.4-11.4%) and unvaccinated vs. indeterminate vaccinated was 6.8% (0.8-12.7%). On adjusted analysis, as compared to unvaccinated patients, at least one dose of vaccine reduced the need for hospitalization (RR: 0.40; 95% CI: 0.35-0.47), oxygen (0.33; 0.27-0.40), NIV (0.23; 0.17-0.32), ICU admission (0.18; 0.12-0.27) and mortality (0.18; 0.11-0.29). Conclusion: Among symptomatic COVID-19 patients, prior vaccination with Covishield (TM) or Covaxin (R) impacted the severity of illness and reduced mortality during a period of widespread delta variant circulation. Full vaccination conferred greater protection than partial vaccination. (C) 2022 Elsevier Ltd. All rights reserved.