S. Mohamed Sabir, M. Khalil Ismail, E. Hassan Ibrahim, and Z. Arshad Khan, “Assessment of Vitamin D Level as a Risk Factor and Illness Severity Indicator in COVID 19 Cases”, HOM, vol. 8, no. 2, Apr. 2022, Accessed: Apr. 10, 2025. [Online]. Available: https://historymedjournal.com/HOM/index.php/medicine/article/view/386