Outbreaks linked to the vaccine, as opposed to the "wild," or naturally occurring, polio virus, are usually stamped out within months.

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Could complicate eradication
Some experts worry the sudden jump in polio cases could complicate eradication efforts. Last year at this time, Nigeria had 54 reported cases caused by wild polio virus.

This year, there have been 106 recorded cases so far, according to new figures released by the World Health Organization and its partners last week.

"This is a huge step backwards," said Oyewale Tomori, a polio expert at Redeemer's University in Nigeria. He said the last time the country had every type of polio was in 1999 and described the current situation as "hugely traumatic."

Since acknowledging last year that some Nigerian children were paralysed by a mutated virus from the oral polio vaccine, health officials have had to use three different vaccines to control the viruses.

The vaccine-sparked outbreak has struck more than 100 children so far, including eight this year. For every paralysed child, there are about 1 000 others infected and spreading the highly infectious and sometimes fatal disease.

Immunisation rates too low
Such outbreaks only happen when immunisation rates are low.

The oral polio vaccine contains a weakened virus. In rare instances, as the virus passes through children who have not been immunised, it changes into a form dangerous enough to ignite new outbreaks.

An injectable polio vaccine is used in the West that does not cause outbreaks, but it is more expensive and must be given by a doctor or nurse.

"There are just way too many kids in Nigeria who haven't been vaccinated and that's allowing the virus to spread," said Dr Bruce Aylward, director of WHO's polio department.

Boycott blamed
Ending the country's parallel polio outbreaks simply requires more vaccine. Nearly all of the children paralyzed by polio are in northern Nigeria, where a yearlong boycott of the vaccine in 2003 triggered an explosion of the disease, which was exported to more than two dozen countries worldwide.

Hard-line Nigerian Islamic clerics called for the boycott, claiming that an immunisation campaign was part of a US-led plot to render Nigerian Muslims infertile or infect them with AIDS.

While Nigerian authorities formally reversed the vaccine boycott, the health system remains weak and there are lingering fears that the vaccine is a Western plot to sterilise Muslims.

Up to 30 percent of children in the north have never had a single dose of polio vaccine, according to the WHO.

When doctors attempt to eradicate a disease, more than 90 percent of a population must be immunised, and about four doses of polio vaccine are needed in Nigeria for children to be protected.

Lack of reach
"Our main problem is operational," Aylward said. "Most kids just lie beyond the reach of the Health Ministry." Aylward said that vaccine-sparked outbreaks are much easier to contain than those caused by wild viruses. Similar outbreaks have happened elsewhere, including China, Indonesia and Madagascar. In Egypt, a vaccine-caused outbreak lasted about a decade.

In a report to be submitted to the World Health Assembly in May, WHO's ruling body, the agency states that the annual risk of a vaccine-caused outbreak ranges from 60 to 95 percent as long as the world continues to use the oral vaccine.

Some experts wonder if the world's reliance on the oral vaccine may ultimately produce more problems as the globe edges toward eradication of polio.

"It is a worry because we've seen these outbreaks happen in a number of countries," said Olen Kew, a polio virologist at the US Centres for Disease Control and Prevention. "But we are aware of the risks and trying to deal with the difficulties." Countries with little or no polio may also take a medical gamble by deciding to spend their money elsewhere.

"As countries slip back on their polio vaccination, they become ripe for outbreaks," said Dr Neal Halsey, a polio and vaccine safety expert at the Johns Hopkins Bloomberg School of Public Health.

Halsey and others think using the injectable vaccine, in addition to the oral vaccine, might solve the problem. WHO has acknowledged that countries must stop using the oral vaccine as soon as possible because of its risks (the vaccine also causes about 250 to 500 cases of polio a year), but says more research is needed.

Entire world vulnerable
In the meantime, officials say that the large numbers of unvaccinated children in Nigeria make the entire world vulnerable to polio. While much progress has been made in the other three countries where polio is endemic - Afghanistan, Pakistan, and India - the surge in cases in Nigeria could undo all of that.

"The outbreak in Nigeria is a shared global problem," Aylward said.

"Until it is stopped in Nigeria, we are all at risk." – (Sapa-AP)

Read more:
A-Z of Polio

April 2008
 

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