Sofia Shoukat, Maheen Saad, Muhammad Razaq, Nadia Qazi, Jahangir Zaib, and Tahira Jehangir. “Role of Pneumococcal and Influenza Vaccine in Prevention and Vitamin E With Beta Carotene in Treatment of Pneumonia in Patients With COPD”. Pakistan Journal of Chest Medicine, vol. 28, no. 1, Mar. 2022, pp. 13-19, https://www.pjcm.net/index.php/pjcm/article/view/849.