Polio is an enduring torment for Zhang Yiming, who lives in a village in Jiangsu province. His younger brother wasn't given a polio vaccine in infancy and contracted the disease in early life, leaving the 30-something unable to walk or even stand without assistance.

The cost of treating the disease quickly ruined the family. "Throughout my five years at primary school, I wore a pair of my father's shoes. They were far too big, but my parents couldn't afford another pair," Zhang said.

Unkind comments from local children added to the family's distress. "Some of the kids shouted at us, saying my brother was an idiot because he couldn't move without a wheelchair," Zhang said.

To give his youngest son an idea of life beyond the village boundary, Zhang's father bought a television set with money that had been earmarked for the elder boy's tuition fees.

"I ran to the TV shop, holding my dad's leg tightly and begging him to let me continue my studies," Zhang said. "It was one of the saddest moments in my life and I'll never forget it. I hated polio very much after that. Some people may not understand how important a small shot of vaccine can be, but my family does."