POLIO is spreading across Africa, even after Bill Gates donated $700m to eradicate it. Part of the problem is an old conspiracy theory that stops people getting inoculated:

In 2003, Islamic leaders in northern Nigeria spread rumors that polio vaccines sterilized Muslim girls. Leaders halted vaccinations, allowing the virus to spread. The WHO said the virus eventually infected 20 countries. By the start of last year, Nigeria was home to half of the world's 1,600 polio cases.

In 1979, mankind eradicated smallpox by inoculating so many people that the virus had nowhere left to hide. In theory, we can do the same to polio, a horrible disease that paralyses children. But the final stages of any eradication programme are always the hardest. I remember watching the World Health Organisation trying to vaccinate children in war-stricken Somalia:

To reach more dangerous areas, the vaccinators wait for a gap in the fighting, and then pounce. There is a polio officer in every district. Some sleep in a different house each night to avoid kidnap, for people with foreign employers are assumed to be rich. Whenever it looks safe enough to fly in the coolboxes, they shout.

With victory elusive and many other global health problems clamouring for donors' money, the WHO is going to adjust its anti-polio strategy soon. It costs a lot to keep jabbing vaccinating babies to prevent a disease that currently claims relatively few victims. But if they eradicate the virus, that's it. All the money now spent on polio can be used for other things.