A Causal Inference of the Effect of Vaccination on COVID-19 Disease Severity and Need for Intensive Care Unit Admission Among Hospitalized Patients in an African Setting

Abstract

ABSTRACTBackgroundThe COVID-19 pandemic is a respiratory illness that has spread to over 210 countries and killed over 6 million people. There is no specific treatment for COVID-19, but vaccines have been developed that can help prevent severe illness and death. A number of studies have investigated the effect of vaccination on disease severity and outcome, and the findings indicate that vaccination is linked to a significant reduction in the risk of hospitalization, intensive care unit admission, and death from the disease. However, there is a scarcity of evidence in Africa in general, and no similar study has been conducted in Ethiopia yet. Therefore, the study aimed to assess the effect of vaccination on COVID-19 disease severity and need for Intensive Care Unit (ICU) admission among hospitalized patients at a private specialty clinic in Ethiopia.MethodsA retrospective cohort study was conducted among 126 patients with COVID-19, 41 vaccinated and 85 unvaccinated, who were hospitalized between September 2021 and May 2022. Data was summarized using frequency (percentage) and median (interquartile range). To compare the characteristics of the two groups, Chi-square/ Fisher’s Exact and Mann Whitney U tests at p-value of ≤ 0.05 were used. To identify the effect of vaccination on COVID-19 disease severity, Marginal Structural Model (MSM) with inverse probability weighting (IPW) approach using robust poisson regression model was fitted and adjusted relative risk (ARR) and 95% CI for ARR were used for interpreting the result.ResultsThe cohort included groups that were fairly comparable in terms of their sociodemographic and clinical characteristics. More than half of the participants were older than 60 years (52.4%), were males (56.3%) and had one or more comorbid illness (52.4%). At admission 85 (67.5%) had severe disease and 11 (8.7%) progressed after hospitalization and required ICU admission, of which three unvaccinated cases died. From the final model, vaccination was found to be associated with a 62% decreased risk of developing severe COVID-19 disease if infected, compared to not getting vaccinated (ARR=0.38, 95% CI=0.23-0.65, p<0.0001).ConclusionsThe study’s findings support previous reports that vaccinated people are less likely to develop severe COVID-19 disease if infected with the virus, emphasizing the importance of continuing efforts to promote COVID-19 vaccination not only to safeguard individuals but also to confer community-level immunity.