Standard operating procedures: responding to a poliovirus event or outbreak, version 4

Overview

In May 2014, the Director-General of the World Health Organization (WHO) declared the international spread of wild poliovirus a Public Health Emergency of International Concern, following international spread of WPV1 in Africa and Asia. In 2021, a WPV-1 confirmed case was reported from Malawi in the African Region, genetically linked to WPV-1 transmission in Pakistan. This highlights the ongoing risk of WPV-1 international spread until the goal of polio eradication is achieved and that countries should be prepared to respond. Global eradication of wild poliovirus type 2 was certified in 2015 as was the global eradication of wild poliovirus type 3 in 2019. The WHO African Region was certified free from WPV1 in 2020. Detection of any wild poliovirus outside a laboratory or vaccine plant should be considered as a public health emergency. Since the withdrawal of OPV2 from routine immunization in 2016, there has been a global increase in vaccine derived poliovirus type 2 (VDPV2) related to the global fall in population intestinal mucosal immunity to type 2 polioviruses in children born after April 2016. Increasingly the circulation of VDPV2 has affected more and more countries, with international spread now occurring regularly. This situation has led to the maintenance of the polio Public Health Emergency of International Concern.