 In 2018, the GPEI conducted environmental surveillance in 44 countries, 24 of which are in Africa.Among the greatest obstacles to global polio eradication are the lack of basic health infrastructure, which limits vaccine distribution and delivery, the crippling effects of civil war and internal strife, and the sometimes oppositional stance that marginalized communities take against what is perceived as a potentially hostile intervention by outsiders.Another challenge has been maintaining the potency of live (attenuated) vaccines in extremely hot or remote areas.