Background: The SARS-CoV-2 virus causes COVID-19, a respiratory syndrome. It causes inflammation and damages several organs in the body. miRNAs play a role in regulating the infection resulting from SARS-CoV-2. MicroRNA-155, a kind of microRNA linked to viral defences, can affect the immune responses during COVID-19. Objectives: Examination of the involvement of microRNA-155 in the development and severity of COVID-19, as well as finding the correlation between microRNA-155 and viral load (copies/mL) in severe cases of the disease. Materials and Method: A case-control research study was performed between October 2022 and June 2023. It included a cohort of 120 hospitalised individuals with severe cases of COVID-19, together with 115 individuals with mild cases of COVID-19 and apparently healthy individuals. A real-time PCR procedure was applied to determine microRNA-155 expression in the studied groups and the viral load (copies/mL) in severe cases of the disease. Results: MicroRNA-155 was expressed in severe cases threefold more than its expression in mild cases of COVID-19 and healthy individuals. Also, a strong association was demonstrated between microRNA-155 and viral load (copies/mL) in severe COVID-19. Conclusion: MicroRNA-155 could be used as a biomarker for severe COVID-19 conditions and could have a role in disease severity and infectious particles of the virus. Since it is positively correlated with viral load (copies/mL) in severe cases of the disease
