Assessment of COVID-19 vaccine effectiveness in a nation with a low vaccination coverage: insights from real-world data and propensity score matched analyses

Abstract

We conducted a comprehensive evaluation of COVID-19 vaccine effectiveness in reducing mortality rates in a country with a low vaccination coverage. A retrospective cohort study analysed data from 1,048,574 adult (≥ 18) patients spanning from March 2020 to April 2022, using data from the national digital medical record repository. Univariate analysis and logistic regression calculated odds ratios and their significance. Propensity score matching was utilised to strengthen the statistical results. Among the 1,048,574 patients diagnosed with COVID-19, 73% (n = 780,718) were unvaccinated, and 27% (n = 267,856) were reported as fully vaccinated. Unadjusted statistical analyses revealed a significant reduction in mortality rates among the vaccinated cohort (1,608 deaths; 0.6%) compared to the unvaccinated group (40,985 deaths; 5.2%) [OR 0.1090 (95%CI 0.1037 to 0.1146), p < 0.0001]. This outcome was consistent across all subgroups, including patient sex, age group, in-hospital setting, vaccine type, SARS-CoV-2 variant, and high-risk patient groups (i.e. with a solid malignancy, cardiovascular disease, chronic pulmonary disease or diabetes mellitus). Logistic regression revealed that the highest fatal risk was in non-vaccinated males aged >63. Propensity score matching substantiated the observed reduction in mortality rates across the entire vaccinated cohort and within all patient subgroups. Individuals infected with SARS-CoV-2 face an elevated risk of premature mortality. Vaccination, especially when utilising mRNA-based platforms, significantly mitigates this risk, particularly among high-risk populations.