A rare outbreak of polio reflects the Philippines’ poor health care

FOR NINETEEN years the Philippines was free from polio. But in September the announcement came that two children living in provinces 900 miles apart had been paralysed by a vaccine-derived strain of the disease. The strain was also found in sewage and in a waterway. Foreign and domestic health authorities have since jumped into action. The next in a series of immunisation drives starts on January 20th on the southern island of Mindanao.

Oral polio vaccines, such as those used in the Philippines, contain a weakened form of the virus, which lingers in children’s intestines for a short while after they ingest it. During that time the virus is excreted in faeces. In places where sewage is not properly managed, it can soon infect people without immunity. As it spreads from one such person to another the virus from the vaccine mutates, gradually gaining strength. This may take many months or even years. Eventually it evolves into a form that is capable of causing harm.