1.1 Global epidemiology update
Global efforts to eradicate polio began in 1988 and, to date, four of the six World Health Organization (WHO) regions have achieved polio-free certification. Within the remaining two regions with endemic poliomyelitis (African and Eastern Mediterranean), Nigeria, Afghanistan and Pakistan have experienced uninterrupted transmission of wild poliovirus (WPV). Fig. 1–2 show the distribution of WPV and circulating vaccine-derived poliovirus (cVDPV) cases in 2016–2018. While Afghanistan and Pakistan continuously reported cases in all three years, a WPV case was last reported in Nigeria in August 2016.
From 2016 to 2018, 17 circulating vaccine-derived poliovirus (cVDPV) post-switch outbreaks of all three serotypes (occurring after the switch from the trivalent oral poliovirus vaccine (tOPV) to the bivalent oral poliovirus vaccine (bOPV) in April–May 2016 affected nine countries in four regions. Of the 14 circulating vaccine-derived poliovirus type 2 (cVDPV2) outbreaks occurring post-switch, seven were first detected through environmental surveillance (ES). Ensuring polio surveillance reach is sensitive and expansive enough to identify poliovirus circulation in every region and every country is a priority for the Global Polio Eradication Initiative (GPEI) and a prerequisite for the global certification of the eradication of poliomyelitis.
Polio surveillance is complicated by the inability of the GPEI to maintain adequate sensitivity in all countries, especially in regions that have been polio-free for some time. In selected high-risk countries, insecurity and safety issues are key challenges, resulting in pockets of populations persistently missed by surveillance efforts. Notably, several countries have worked to overcome these challenges and improve surveillance reach into inaccessible areas.
To address ongoing challenges, the Global Polio Surveillance Action Plan (GPSAP) 2018–2020 was developed to support countries in evaluating and increasing the sensitivity of their surveillance systems; to share supplemental strategies that may help close the gaps in detecting polioviruses; to strengthen coordination across surveillance field teams, the laboratory and data information systems; and to leverage activities across functional areas to create a more effective, efficient programme and document zero cases worldwide. As part of the GPSAP’s implementation, the plan reviews disease risk and surveillance performance and prioritizes countries for targeted support. In 2018, 29 priority countries were identified for surveillance strengthening per the GPSAP, due to the ongoing or high risk of poliovirus transmission and limited country capacity to adequately address those risks; the prioritization targeted areas in the Eastern Mediterranean and African Regions, the two yet to be certified as WPV-free, but included outbreak-affected countries in non-endemic regions.
This Global Polio Surveillance Status Report, 2019 reviews the state of poliovirus surveillance for the first year of the GPSAP’s implementation, comparing its performance to the preceding two years and taking stock of the challenges faced, innovations advanced and opportunities explored to enhance surveillance especially in priority areas.