Poliomyelitis is a viral infection that can lead to paralysis of the arms, legs or the diaphragm (which controls breathing). Further symptoms – including new weakness, joint and muscle pain and fatigue - can occur years after the initial bout of poliomyelitis. These symptoms are known as 'late effects of polio' or 'post polio syndrome'. Not everyone who has had polio will develop late effects. People who were severely paralysed by polio are more commonly affected. Approximately 20 to 40 per cent of people who had acute paralysis due to polio will develop late effects.