Harahap และ Juliandi. (2000) Factors affecting childhood immunization in North Sumatra province, Indonesia. Mahidol University,:ม.ป.ท.Harahap และ Juliandi. 2000. Factors affecting childhood immunization in North Sumatra province, Indonesia. ม.ป.ท.:Mahidol University,;Harahap และ Juliandi. Factors affecting childhood immunization in North Sumatra province, Indonesia. ม.ป.ท.:Mahidol University, 2000. Print.