Impact of vaccination status on mortality among symptomatic COVID-19 patients during the second wave of the pandemic: a cohort study

• In this cohort of 4183 patients who presented to the emergency department with symptomatic COVID-19 infection during April and May 2021 (the peak period of the second wave), the mortality was 0.2%, 3.5%, 6.2% and 12.9% among fully vaccinated, partially vaccinated, indeterminate and unvaccinated patients respectively. • Prior vaccination impacted severity of infection by reducing the need for oxygen, non-invasive ventilation and intensive care admission. 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® on mortality among symptomatic COVID-19 patients during the second wave of the pandemic in India. 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). 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 Covishield TM and 4.8% (201/4183) had received Covaxin®. 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). Among symptomatic COVID-19 patients, prior vaccination with Covishield TM or Covaxin® impacted the severity of illness and reduced mortality during a period of widespread delta variant circulation. Full vaccination conferred greater protection than partial vaccination.