Suleman, A., R. Ullah, H. Nisar, S. Naz, and R. N. Khan. “Prevalence of Influenza Vaccination in Chronic Obstructive Pulmonary Disease Patients”. Pakistan Journal of Chest Medicine, vol. 24, no. 2, Aug. 2018, pp. 86-90, http://www.pjcm.net/index.php/pjcm/article/view/519.