World Polio Day was on 24 October. Global polio numbers have fallen over decades, but new outbreaks continue to raise questions about eradication efforts in countries where humanitarian access is a problem. The recent surge in polio is fuelled by dozens of cases of wild poliovirus in Pakistan and Afghanistan, and by unexpected new outbreaks of vaccine-derived strains, rare mutations that affect under-immunised populations, in at least 14 other countries. Some of these had not seen polio for years, including Ghana and the Philippines, which both announced outbreaks in September. In some cases, vaccine-derived polio strains have leapt across borders - from Nigeria to its neighbours and from Somalia to Ethiopia. A WHO committee has said, ‘The risk of new outbreaks in other countries is considered extremely high, even probable’. There are grave concerns that it will not be possible to control outbreaks in Africa and Asia.