The World Health Organization wants to certify the world as being polio-free in 2005, but problems with new polio outbreaks caused by vaccination could hamper that goal.
The World Health Organization has done an excellent job at getting polio under control. In 1988 there were 350,000 cases of polio reported worldwide. In 2001, there were only an estimated 600 to 1,000 cases reported.
But that success is also part of the problem. Until the world can be certified as completely free of polio, childhood vaccination must continue. But the oral polio vaccine itself can mutate and start off an outbreak.
The oral polio virus is a version of polio that is far less virulent. But simply through random mutation it an regain that virulence. It also has the ability to borrow genes from other viruses found in children it infects.
Now this sort of mutation would not get very far in societies with high levels of immunization. The problem is that there are parts of the world where vaccination is still only at 80 percent or less, and those areas are susceptible to outbreaks.
In fact just such an outbreak — albeit on a rather small scale — occurred in the Dominican Republic and Haiti in 1999 and again in 2001. As many as 20 percent of children in the Dominican Republic and Haiti are not vaccinated and are susceptible to a mutated version of the oral polio vaccine.
The latest outbreak highlights concerns over how long vaccination should continue after polio is declared eradicated, and also adds new importance and impetus to eradicating the disease as fast as possible to minimize the risk of a widespread outbreak.
Polio vaccine bites back. Tom Clarke, Nature, March 15, 2002.
Promise of eradicating polio experiences setback. National Center for POlicy Analysis, April 16, 2002.