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As Zerospinzone readers know, the eradication of polio has been the target of a massive international effort started in 1988 and led by the World Health Organization, the United Nations Children's Fund and the Rotary Foundation. The effort has been incredibly successful and in fact has pushed the deadly polio virus to the brink of extinction. So far this year there have only been 4 cases of poliomyelitis caused by the wild polio virus. As far as we know, the wild virus hangs by a thread in just two countries, Pakistan and Afghanistan.
Administering the oral polio vaccine
Credit: Michael Tsegaye, Flickr
However, the final eradication of the disease has been complicated by the fact that the weakened polio viruses used in the Oral Polio Vaccine occasionally mutate to a virulent, disease causing form. This kind of mutation is very rare, but with hundreds of millions of doses administered, in recent years there have been more cases of poliomyelitis caused by the mutated vaccine, especially the type 2 vaccine, than caused by the wild virus itself. (The polio virus comes in 3 varieties, each of which has its own vaccine. The type 1 and type 3 viruses appear to have been eradicated, and recent vaccine-derived cases have all come from the type 2 vaccine.
The good news is that researchers have developed a new type 2 oral vaccine--nOPV2--that is genetically much more stable than the earlier version, and so much less likely to mutate to a disease-causing form. The new vaccine successfully snuffed out a recent outbreak of vaccine-derived illness in Tajikistan without leading to any new cases. This successful use of the novel type 2 vaccine provides hope that the few countries where either wild polio virus or disease-causing forms of the older type 2 vaccine still exist can soon join the rest of the world and be certified as completely free of polio.
Then--hopefully very soon--polio will join smallpox as once dread and deadly human diseases that have been permanently wiped from the face of the earth.
