Elnady, Mohamed, Ahmed Abdel Hafeez, Hebatallah Assal, Eman Zaid, and Gihan Abo Elwafa. “Serum Vitamin D Levels and the Severity and Clinical Course of COVID-19”. Monaldi Archives for Chest Disease (September 26, 2024). Accessed November 22, 2024. https://www.monaldi-archives.org/macd/article/view/2978.