Mat, S. N., N. Ismail, S. Taib, H. F. Ghazi, Z. I. Azhar, M. S. Jeffree, A. Mohammed Nawi, and M. R. Hassan. “Acceptance Factors of Pneumococcal Vaccination Among Adult Population: A Systematic Review”. International Journal of Public Health Research, vol. 8, no. 2, Sept. 2018, pp. 1006-14, https://spaj.ukm.my/ijphr/index.php/ijphr/article/view/222.