WHO fighting to eradicate wild polio virus

"Genetic sleuthing" has revealed that a dose of oral polio vaccine is capable of reverting to the deadly polio virus and causing an outbreak, the UK-based science magazine, Nature, reported in a recent edition. That a weakened form of the polio virus, called OPV, which is given to children as a vaccine, can revert to a virulent form has been known since its creation, experts agree. But only recently has this fact become a problem: widespread eradication means that susceptibility to the virus is on the increase. In 2000, an outbreak of the wild polio virus occurred on the Caribbean island of Hispaniola, killing two children and paralysing a further 19. From the genetic sequence of virus samples from each of these children, virologists at the US Center for Disease Control and Prevention in Atlanta, Georgia, discovered the origin of the virus: a single dose of OPV, given to a single child. The genes crucial to the development of the polio virus which are normally "switched off" in the vaccine, had "switched back on" in the Hispaniola virus, probably through random mutation, Nature reported. Children on the island were more susceptible to the virus because a significant proportion of them had not been vaccinated fully. Moreover, people had become "more relaxed" about vaccinating their children, because the area had been officially designated a "polio-free zone," Elias Durry, the World Health Organisation (WHO) Polio Coordinator for the Horn of Africa, told IRIN on Friday. The conditions for the outbreak were therefore perfect. What this means for the current worldwide polio vaccination campaign is that OPV must be given to all children under five years of age as quickly as possible in unvaccinated areas. "The problem lies not with the vaccine, but with the system that doesn't allow children to receive the vaccine," Durry said. Currently the 10 countries where wild polio virus is still endemic are characterised by either being extremely highly populated - such as India, Pakistan or Afghanistan - or war-torn - such as Angola, Sudan and Democratic Republic of the Congo. "Lack of access to areas in war-torn countries is a big problem," said Durry. "In order to vaccinate every single child under five years of age, every single part of a given country has to be reached." WHO aims to have interrupted transmission of the virus by the end of 2002, to be able to certify the world as being free of the wild polio virus by 2005, and to subsequently withdraw OPV from use. In its quest to achieve this, started in 1999, the organisation has significantly stepped up its anti-polio campaign to include house-to-house vaccinations in rural areas, improved surveillance of symptoms and increased rounds of vaccinations. Referring to the case in Hispaniola, Durry said: "It is a worry, but it also gives us the impetus to continue the job we are doing, which is the eradication of the virus... If a case similar to that in Hispaniola occurs again, it's not a problem. We will simply move into the area and vaccinate everyone fully." In 2000 there were 675 cases of wild polio virus infection in the world, WHO reports, which were reduced to 473 in 2001.