Chacon-Cruz, Enrique, Erika Zoe Lopatynsky-Reyes, & Yodira Guadalupe Hernandez-Ruiz. " Vaccination: A Legacy of Success and Persistent Challenges, 50 Years Since the Launch of the Expanded Programme on Immunization." Medical Research Archives [Online], 13.3 (2025): n. pag. Web. 21 Apr. 2025