The sensitivity of acute flaccid paralysis surveillance - the case of South Sudan: retrospective secondary analysis of AFP surveillance data 2014-2019

INTRODUCTION: South Sudan has made quite impressive progress in interrupting wild poliovirus and maintaining a polio-free status since the last case was reported in 2009. South Sudan introduced different complementary strategies to enhance acute flaccid paralysis (AFP) surveillance. Hence, the objective of this study is to evaluate the sensitivity of the surveillance system using the WHO recommended surveillance standard and highlight the progress and challenges over the years. METHODS: we conducted a retrospective, descriptive, quantitative study design and used the available secondary AFP surveillance database. RESULTS: the overall non-polio AFP rate was 6.2/100,000 children under 15 years old in the study period. The stool adequacy was maintained well above the certification level of surveillance. The two main surveillance performance indicators were met at the national level throughout the study period. In contrast, only five out of ten states persistently attained and maintained the two main surveillance performance indicators throughout the study period, while in 2019 all states achieved except for Jonglei state. During the analysis period, no wild poliovirus was isolated except two circulating Vaccine Derived Poliovirus Type 2 (cVDPV2) cases in 2014 and one Immunodeficiency Vaccine Derived Poliovirus Type 2 (iVDPV2) case in 2015. However, on average, three cases were classified as polio compatible with each year of the study. CONCLUSION: South Sudan met the two key surveillance performance indicators and had a sensitive AFP surveillance system during the period studied. We recommend intensifying surveillance activities in the former conflict-affected states and counties to maintain polio-free status.