Poliomyelitis (polio) is a highly infectious disease caused by a virus. It invades the nervous system, and can cause total paralysis in a matter of hours.

Until the 1950s, polio crippled thousands of children every year in industrialised countries. Soon after the introduction of effective vaccines in the late 1950s (IPV) and early 1960s (OPV), polio was brought under control, and practically eliminated as a public health problem in industrialised countries.

It took somewhat longer for polio to be recognised as a major problem in developing countries. However, ‘lameness surveys' during the 1970s revealed that the disease was also frequent in developing countries, crippling thousands of children every year. As a result, during the 1970s routine immunisation with OPV as part of national immunisation programmes (Expanded Programme on Immunisation, or EPI programmes) was introduced worldwide, helping to control the disease in many developing countries.

Today, the disease has been eliminated from most of the world, and only three countries worldwide remain polio-endemic (Nigeria, Pakistan and Afghanistan).