WHO News

Polio virus pops up in unexpected places

On three occasions since June last year the polio virus has made impromptu appearances that have given the international health community food for thought.

First, in June it was found in tap water in the eastern French town of Strasbourg. On the strength of preliminary analysis, WHO believes that this virus came from an old vaccine strain that possibly escaped from a laboratory. ‘‘This event underlines the need for all laboratories to begin implementing WHO’s plan for worldwide containment of laboratory poliovirus,’’ commented Bruce Aylward, who heads WHO’s polio eradication team.

Then in July, the virus appeared in the Dominican Republic and Haiti, where it had by 22 December caused 8 confirmed cases of polio, with two deaths. The responsible virus was identified as originating from an oral polio vaccine virus that had ‘‘reverted’’ to a virulent form and spread in an incompletely vaccinated community. This is the first outbreak of polio in the Americas since the disease was certified in 1994 as eradicated from the region. ‘‘The outbreak is being properly investigated and controlled and should not affect the certification,’’ Dr Alwyard said.

Finally, in August, an outbreak of polio occurred in the West African island of Cape Verde, and had caused 44 cases by 22 December. On the strength of molecular analysis, WHO officials believe this outbreak was caused by a wild poliovirus, probably imported from Angola, where transmission of the infection is still occurring.

These two outbreaks, Dr Ayward said, ‘‘tell us first that we will eventually have to stop immunization with the oral polio vaccine once polio has been globally certified as eradicated and that we will have to do so in a globally coordinated manner so that no country remains vulnerable. Until that time, high oral polio vaccine coverage must be maintained.’’ Dr Aylward added: ‘‘They also tell us that the vaccine virus and not just wild poliovirus will have to be rigorously contained after eradication and that thorough polio surveillance will have to continue for quite a number of years not only after eradication but also after the cessation of immunization.’’

John Maurice,

World Health Organization Genebra - Genebra - Switzerland
E-mail: bulletin@who.int