The evolution of Tanzania's poliomyelitis surveillance system since the introduction of the expanded program on immunization in 1975

Introduction: Tanzania's Expanded Programme on Immunization (EPI), launched in 1975, aimed to combat several diseases, including polio. Despite initial challenges, significant improvements were made in the 1980s, leading to increased vaccination coverage and a decline in disease incidence, with the last wild poliovirus case reported in 1996 and further strengthened efforts through the NSTOP initiative in 2012. Methods: we conducted a descriptive study analyzing AFP surveillance data in Tanzania from 1980 to 2024, using records from the Ministry of Health and WHO. The study assessed surveillance performance with WHO indicators, noting that EPI services expanded to all regions by 1980 after joint evaluations and infrastructure improvements. Results: from 1980 to 1994, 1,576 wild polioviruses were reported, with 70.3% occurring between 1985 and 1987. Vaccination coverage was low, with OPV3 below 50% and DTPw3 below 60%. During 1995-2000, only four wild polioviruses were isolated, with improved vaccination coverage. From 2001 to 2014, no wild poliovirus was isolated, and surveillance indicators improved significantly. In the post-polio-free certification phase (2016-2024), fifteen cVDPV2 variants were reported, with high vaccination coverage and robust environmental surveillance. From 1980 to 2023, significant improvements in vaccination coverage for measles, diphtheria, and tetanus were observed, reflecting progress in public health initiatives. Conclusion: since the initiation of the EPI, Tanzania has significantly improved the sensitivity and quality of its polio surveillance system. The evolution from aggregate to case-based laboratory surveillance highlights the program's impact on disease detection and serves as a model for other vaccine-preventable diseases, with potential further enhancements through expanded environmental surveillance.