W. Issa , Y., and S. M. Salih. “Evaluating the Effectiveness of Pfizer, AstraZeneca, and Sinopharm Vaccines Against COVID-19 in Iraq: A Cross-Sectional Study of Vaccine Efficacy and Symptom Severity”. Journal of Madenat Alelem University College, Vol. 16, no. 1, May 2024, pp. 11-21, https://journal.mauc.edu.iq/index.php/JMAUC/article/view/507.