Successes and challenges of expansion of environmental poliovirus surveillance in the WHO South-East Asia Region
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World Health Organization. Regional Office for South-East Asia
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The last decade has witnessed an exponential expansion of environmental surveillance (ES) ofpoliovirus in sewage samples in the World Health Organization (WHO) South-East Asia Region. Thishas grown from only three sites in Mumbai, India in 2001 to 56 sites in 2017 in Bangladesh, India,Indonesia, Myanmar, Nepal and Thailand. ES is critical to the region in providing evidence of silenttransmission of vaccine-derived poliovirus and Sabin-like poliovirus type 2 – especially since the global“switch” to cease use of oral polio vaccine type 2 – and for monitoring the effectiveness of containmentactivities. This targeted expansion of ES to supplement surveillance for acute flaccid paralysis (AFP)required quality assurance in ES procedures, improvements in the sensitivity of the laboratory-basedsurveillance system, and establishment of real-time data analysis for evidence-based programmes.ES in the region has provided documentary evidence for the absence of indigenous wild poliovirusin circulation and no importations via international travellers. Post-switch, while no vaccine-derivedpoliovirus was detected from AFP cases, ES identified five ambiguous vaccine-derived polioviruses in2016 and early 2017, with no evidence of circulation. Future challenges include monitoring for vaccinederived poliovirus strains shed for a prolonged time by immunodeficient individuals, and expandingES to areas lacking sewage networks. To maintain the polio-free status of the WHO South-EastAsia Region and achieve a world free of poliomyelitis, critical evaluation of immunization coverage,continued performance of surveillance for acute flaccid paralysis, and enhanced analysis of sewagesamples to detect any breach in containment are essential.
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