© UN Photo   In 1960, an Indian boy in Bombay, paralysed by polio, learns to walk again. In 1971, children play football at a paralysis rehabilitation centre in Gatagara, Rwanda. Surveys in Africa in 1977 indicate that developing countries have polio infection rates comparable to those found in richer countries before the invention of the vaccines. However, amid widespread disease of all kinds, polio paralysis often goes unnoticed. © UNICEF/ICEF6293/Alastair Matheson