Analysis of five major multicenter studies spanning multiple years reveals a dramatic epidemiological shift in severe childhood diarrhea patterns. Pre-rotavirus vaccination, rotavirus caused 22-28% of moderate-to-severe diarrhea cases in 6-11-month-olds. Following vaccine introduction, rotavirus's contribution dropped to 10-11% across Africa and Asia, while Shigella bacterial infections emerged as the dominant cause, responsible for one-third to one-half of cases in children aged 12-35 months. The research also documented encouraging mortality trends, with 90-day case fatality rates declining from 2.21% to 0.30% over the study period. This epidemiological transition has profound implications for pediatric health strategies in developing nations. The Shigella predominance suggests urgent need for improved sanitation infrastructure and potential Shigella vaccine development, as bacterial pathogens showed higher mortality rates (2.52%) than viral causes (1.42%). However, this preprint analysis awaits peer review, and results may change. The findings represent confirmatory evidence of rotavirus vaccine effectiveness while highlighting an emerging bacterial disease burden that could reshape global child health priorities and resource allocation in low-income settings.