Poliomyelitis (polio) is a highly infectious viral disease that mainly affects young children. The virus is transmitted through contaminated food and water, and multiplies in the intestine, from where it can ultimately invade the nervous system. Many infected people have no symptoms, but excrete the virus in their faeces, hence transmitting infection to others.
Initial symptoms of poliovirus infection include fever, fatigue, headache, vomiting, stiffness in the neck, and pain in the limbs. In a small proportion of cases, the disease causes paralysis, which is often permanent. Polio can only be prevented by immunization.
China had its last indigenous polio case in 1994 and was certificated as a polo-free country by the Regional Commission for the Certification of Poliomyelitis Eradication (RCC) in the WHO Western Pacific Region in 2000. However, between July and October 2011, China experienced an outbreak caused by imported wild poliovirus type 1 (WPV1) from Pakistan. This outbreak paralyzed a total of 21 people in four prefectures of Xinjiang. With a tremendous effort vaccinating the vulnerable population, China successfully interrupted transmission of the virus and stopped the outbreak.