Polio returns to threaten world plan for eradication

Tim Radford, science editor
Friday January 19, 2001
The Guardian

A small group of sick children in the Dominican Republic and Haiti could pose a threat to one of the World Health Organisation's most cherished plans - the eradication of the crippling and often lethal disease poliomyelitis, or polio.

Since October, there have been 45 cases of paralysis on the Caribbean island of Hispaniola, six years after the Pan American Health Organisation declared polio eradicated in the Americas.

Laboratory analysis of the infections, according to the science journal Nature yesterday, produced an alarming find: The polio cases could have developed not from the virus that doctors tried to eradicate, but from a mutated form of their vaccine.

In 1979 the WHO, charities, scientists and national health groups combined to wipe out one of humanity's most terrifying scourges: smallpox. In 1988 the WHO launched a similar assault on another virus that replicates only in humans: polio.

The aim was to vaccinate every child on the planet by 2000 and declare the virus extinct by about 2005, a few years after the last recorded case.

The timetable, however, slipped - interrupted by civil and national wars, natural disaster and political upheaval. But the cases of polio were reduced to around 2,000 last year from 350,000 in 1988.

Teams of experts and volunteers "swamped" whole regions of Asia, Africa, the Pacific and South America in an effort to immunise all children on the same day with an oral vaccine developed by Albert Sabin more than 40 years ago.

The vaccine was a "weakened" form of the virus, which multiplies and triggers resistance against itself, before spreading into the local water supply; polio is a waterborne disease. The theory was, in places with poor hygiene, any children who missed immunisation would "catch" the weakened virus rather than the dangerous one, and be immunised as a result.

But according to Nature, seven new cases of polio have been confirmed on the island of Hispaniola: six in the Dominican Republic, and one across the border in Haiti.

Their discovery led the US Centres for Disease Control (CDC) in Atlanta, Georgia, to conclude that they were caused by a mutation in the vaccine. That is, the weakened version had not only regained its virulence, it had recovered the ability to spread from person to person.

The next step for WHO chiefs is to work out how it happened. There have been very few such cases in four decades of oral vaccination.

Only one child in five in the Constanza region of the Dominican Republic received any of the three doses needed for immunisation; there was a large, vulnerable population.

"My assumption is that this is an unusual event," Donald Henderson of Johns Hopkins University, the architect of the smallpox eradication programme, told Nature. "It can't be occurring with great frequency otherwise we would have seen it a long time ago."

But the implication is that polio may be more difficult to eliminate than anyone had thought. "Clearly," Roland Sutter of the CDC said, "this is raising a red flag."

Printable version | Send it to a friend | Read it later | See saved stories