West African Child Is Paralyzed by Vaccine-Derived Polio

A case of vaccine-derived polio has paralyzed a child in Bamako, the capital of Mali, and an emergency vaccination drive is being organized to forestall an outbreak, the World Health Organization announced Monday.

It is the first time the disease has been seen in Mali since 2011. The patient is a Guinean child whose parents traveled to Bamako seeking medical care. The child’s virus is a close genetic match to a strain last detected in a nearby region of Guinea in 2014.

The child was not infected with the “wild type” polio virus, which the W.H.O. says has been eliminated from Africa. No cases of paralysis from wild virus have been found in Africa in a year, but it takes three years before a region is declared polio-free.

Rather, it was a strain created when one of the three live, weakened 

virus strains in the oral polio vaccine mutated to become dangerous again. Such mutations are a rare but persistent consequence of relying on oral polio vaccine drops, which are easy to administer and much more protective than so-called killed vaccine.

Killed vaccine cannot mutate, but must be injected by medical professionals, who are in short supply in developing countries. Also, blood-borne diseases like hepatitis can be spread if the injectors are not carefully supervised and needles are reused.

There were 55 cases of vaccine-derived polio paralysis in the world in 2014 and 66 in 2013. There had been 12 this year before the Malian one. Nine were on the island nation of Madagascar, one was found in Nigeria, and last week the W.H.O. announced that two children in western Ukraine had been paralyzed.

Outbreaks of vaccine-derived virus are normally contained by doing several successive rounds of vaccination in areas surrounding the known cases.

The virus may have circulated undetected in Guinea for months because frozen stool samples were not shipped during the Ebola outbreak, said Dr. Hamid S. Jafari, the W.H.O.’s director of polio eradication.

For the first vaccination round, “the plan is to go big and go aggressive.” Dr. Jafari added. The goal is three mass vaccination rounds in less than 120 days, and he said he thought that was possible because many W.H.O. and United Nations staff members were already in the area and the country’s Health Ministry was already on high alert because of Ebola, but there have been no Ebola cases in eastern Guinea for many months.