Estimation of the effect of vaccination in critically ill COVID-19 patients, analysis using propensity score matching.

Background: Vaccination helped in reducing mortality and disease severity due to COVID-19. Some patients can develop breakthrough infections. The effect of vaccination in critically ill patients admitted with breakthrough infections is not well studied. We designed a study to estimate the effect of vaccination on ICU mortality in critically ill COVID-19 patients by using propensity score matching.

Methods: We included patients from 15th June 2020 to 31st December 2021. Inclusion criteria were unvaccinated and vaccinated COVID-19 patients requiring intensive care unit (ICU) admission. The institutional ethics committee approval was obtained (institutional ethics committee, IEC 08/2023, Clinical trial registry, India CTRI/2023/01/049142). The primary outcome was ICU mortality. The secondary outcomes were the length of ICU stay and duration of mechanical ventilation. We used multivariable logistic regression (MLR) and propensity score matching (PSM) for the statistical analysis.

Results: Total of 667 patients (79.31%) were unvaccinated and 174 (20.68%) vaccinated. The mean age was 57.11 [standard deviation (SD) 15.13], and 70.27% were males. The ICU mortality was 56.60% [95% confidence interval (CI) 53.24-60%]. The results of MLR and PSM method showed that vaccinated patients were less likely to be associated with mortality [adjusted odds ratio (AOR), 95% CI using logistic regression: 0.52 (0.29, 0.94), and by propensity score matching: 0.83 (0.77, 0.91)].

Conclusion: The findings of this study support COVID-19 vaccination as an effective method for reducing case fatality not only in the general population but also in critically ill patients, and it has important public health implications.