Ramayani, Oke, Ridwan Daulay, Sri Sofyani, and Iskandar Lubis. “Factors Related to Missed Opportunities for Immunization at Urban and Suburban Primary Health Centers in Medan”. Paediatrica Indonesiana 47, no. 1 (February 28, 2007): 21-6. Accessed April 28, 2024. https://paediatricaindonesiana.org/index.php/paediatrica-indonesiana/article/view/337.