 Polio is a cruel disease. Children, pregnant women, and people with weakened immune systems are especially susceptible to the virus, which attacks the brain and spinal cord. One in every 200 children infected suffers paralysis. Only vaccination can stop the spread of this incurable and highly contagious disease. While vaccinations have eliminated infections in most of the world, the virus persists in a few places, including parts of Afghanistan, Pakistan, and Northern Nigeria. Since 1988, the Global Polio Eradication Initiative, or GPEI, has combined the efforts of governmental and non-governmental organizations, private businesses, and major philanthropies to vaccinate every child in the world. This is a story of how geospatial technologies helped make a difference in vaccinating kids in remote parts of Northern Nigeria. One instrumental organization in the fight against polio in West Africa is the non-profit eHealth Africa. eHealth Africa uses technology to improve healthcare management, and cites GIS as one of its core competencies. GIS manager Dami Sonoike spoke with me in 2016 about the role of GIS in the eradication of polio in Nigeria. Dami has a BS in surveying and geoinformatics from the University of Lagos and an MS in Geographic Information Science from University College London. He leads a team of about 21 GIS professionals at eHealth Africa. The challenge, Dami explained, was finding the children who needed vaccinations. Northern Nigeria is big. Its many small villages were poorly mapped when eHealth Africa joined forces with the GPEI in 2014. The first step in locating the children was to acquire high-resolution satellite imagery of the region. This was done with support from the Bill and Melinda Gates Foundation. Imagery enabled Dami's team to identify buildings and rural settlements, as well as roads and waterways. But imagery alone wasn't sufficient for the job the eHealth Africa GIS team needed to do. They needed to extract information from the imagery by delineating settlement boundaries and other features, associating features with place names, and pinpointing individual dwellings for visits by vaccinators. For these tasks and others, Dami said, his team had to learn to digitize. Once the eHealth Africa GIS team had digitized the key vector features needed to dispatch vaccination teams, they set up a procedure to track the villages they visited and the households where they vaccinated children. Vaccinators used the new maps to navigate to target villages. They carried mobile phones equipped with GPS receivers that recorded their locations every few minutes. When vaccinators returned to their GIS field station, staff copied the GPS waypoints from the phones to eHealth Africa's distributed data management system. To assure proper vaccination coverage, GIS analysts overlaid the digitized maps with digital grids and with the GPS waypoints downloaded from the mobile phones. By calculating the frequencies of waypoints in each grid cell, analysts were able to validate vaccinations and to dispatch follow-up vaccination teams if necessary. Geospatial technology, data, and methods are just one aspect of the international efforts to eradicate polio and other infectious diseases. Even so, their impact has been profound. Tope Bello, product manager with Esri's professional services and an advisor to eHealth Africa, says he is absolutely certain that the reduction of polio cases in Nigeria from 122 in 2012 to 0 in 2015 could not have been achieved without GIS. According to the Centers for Disease Control and Prevention, polio incidents declined 99% worldwide since the Global Polio Eradication Initiative began in 1988. In Nigeria, no new cases were reported from July 2014 until 2016 when wild polio virus was discovered in the Guoza and Jere local government areas in the northern state of Borno. Some blame the failure to completely eradicate polio in Nigeria on flagging government-run vaccination programs. New immunization programs have since been announced. Protecting children from polio and other infectious diseases requires vigilance. One lesson learned from eHealth Africa's experience is that GIS can help NGOs and governments conduct rigorous and effective vaccination programs in the most challenging settings on Earth to protect children's health.