Efficacy of COVID-19 vaccination on severe acute respiratory infections (SARI): epidemiology and clinical outcomes in hospitalized patients in Benin

SARS-CoV-2 infection, although initially respiratory, can evolve into a severe systemic disease marked by dysregulated inflammation and coagulation disorders. While COVID-19 vaccination is well established in reducing mortality, its effect on preventing specific clinical complications among hospitalized patients remains insufficiently documented. This study assessed the impact of COVID-19 vaccination on major clinical complications—including altered level of consciousness, respiratory distress, anemia, thromboembolic disorders, and renal failure—among patients hospitalized for Severe Acute Respiratory Infection (SARI) in Benin. A prospective analytical cohort study was conducted over a five-month period in four referral hospitals, enrolling 612 patients with laboratory-confirmed SARS-CoV-2 infection, of whom 19.6% were vaccinated and the mean age was 57 years. Vaccination status was the primary exposure variable, and multivariate logistic regression analyses were performed for each complication, adjusting for age, sex, and comorbidities. After adjustment, vaccination was significantly associated with a reduced risk of anemia (adjusted OR = 0.68; p = 0.030) and thromboembolic disorders (adjusted OR = 0.45; p = 0.030). No statistically significant associations were observed for renal failure (p = 0.290) or altered mental status (p = 0.360). In contrast, vaccination was associated with increased odds of respiratory distress (adjusted OR = 1.69; p = 0.031), a paradoxical finding likely attributable to hospitalization-related selection bias (Berkson’s bias), as vaccinated individuals admitted for SARI represent a higher-risk subgroup. Overall, COVID-19 vaccination appears to modify the clinical profile of severe disease by reducing the risk of hematological and thromboembolic complications, underscoring its role in mitigating the systemic severity of SARS-CoV-2 infection even among patients requiring hospitalization. Keywords: SARS-CoV-2, Vaccination, Severe acute respiratory infections (SARI), Clinical outcomes, Benin.