Impact of prior vaccination with CovishieldTM 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

Abstract

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™ or Bharath Biotech's Covaxin® 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 Covishield™ 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).

Conclusion: Among symptomatic COVID-19 patients, prior vaccination with Covishield ™ 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.

Keywords: COVID-19; Corona virus; Covaxin®; Covishield™; Mortality; Vaccination.

Fig. 1

STROBE diagram showing the outcome among fully vaccinated, partially vaccinated and unvaccinated patients Of the 4183 patients who presented during the study period, among the 403 fully vaccinated patients, one patient died (2%), while among the 451 partially vaccinated patients 17 died (11.4%) and 418 (20.6%) died among the unvaccinated group (n = 3234). The mortality was 18.2% (4/65) in the indeterminate vaccination status group. More patients were managed on home isolation among fully vaccinated (88%) that among unvaccinated (37.1%).

Fig. 2

Forest plot illustrating the adjusted effect of partial and full vaccination, compared to unvaccinated patients, on illness severity and mortality 2a: Forest plots demonstrating the adjusted effect of partial vaccination versus unvaccinated individuals on proportion presenting with Sequential Organ Failure Assessment (SOFA) score > 4 and need for oxygen in hospital, non-invasive ventilation, hospitalization, intensive care unit (ICU) admission and mortality, expressed as risk ratio (RR) with 95% confidence intervals (CI). Partial vaccination was associated with significantly reduced risk (p < 0.001) in mortality and morbidity parameters when compared with unvaccinated individuals. 2b: Forest plots demonstrating the effect of full vaccination versus unvaccinated individuals on proportion presenting with SOFA score > 4 and need for oxygen in hospital, non-invasive ventilation, hospitalization, ICU admission and mortality, expressed as risk ratio (RR) with 95% confidence intervals (CI). Full vaccination was associated with significantly reduced risk (p < 0.001) in mortality and morbidity parameters when compared with unvaccinated individuals.