In Kenya's sparsely populated northern counties of Samburu and Turkana, community health volunteers are mounting motorbike patrols into remote and nomadic settlements to investigate reports of sudden paralysis in children — a potential sign of vaccine-derived poliovirus, a mutated strain of the weakened virus used in oral vaccines that can spread where immunisation rates are low. While Nairobi uses wastewater testing to detect the virus early, that system cannot function in areas without sewers, leaving volunteers like Eroi Lemarkat as the frontline defence, racing to collect stool samples within a 14-day window before the chance of detection is lost. The effort is further complicated by nomadic pastoralist families who regularly cross into Somalia, requiring cross-border coordination to ensure no child goes undetected — a challenge that health officials say hinges as much on community trust as on laboratory science.