An Indian child is vaccinated against polio

A large outbreak in India accounted for most of the increase.

India is one of seven countries where the disease is still endemic.

But there has been some success in the fight against polio with Ethiopia, Sudan and Angola, where the virus had been endemic, declared polio-free in 2002.

Access to children in Somalia and Afghanistan for vaccination has also improved.

The World Health Organization hopes to completely wipe out polio by 2005.

Paralysis

Figures from the US Centers for Disease Control and Prevention showed there were 1,920 confirmed cases of polio reported by laboratories in 2002, up from 483 the previous year.

The disease, which once affected millions of children, attacks the central nervous system, often causing paralysis, muscular atrophy and deformity. Between 5 and 10% of those infected die when their breathing muscles become paralyzed.

It is usually contracted through exposure to contaminated water.

Polio has disappeared from most the Western countries following vaccination programs begun in the 1950s.

But it still exists in some Asian and African countries.

Nigeria, Egypt, Somalia, Niger, Pakistan and Afghanistan all reported polio cases in 2002.

The Indian outbreak centred on the states of Uttar Pradesh and Bihar. Cases there accounted for 71% of all those seen across the world in 2002.

It was the worst outbreak since 1988 when the World Health Organization began its bid to totally eradicate polio using mass vaccination campaigns.

In a bid to prevent another outbreak in the country, the WHO and Indian authorities launched a huge vaccination campaign to inoculate an estimated 80 million children in six Indian states in April.

More campaigns are planned for next year.

Vaccinations

There are two forms of polio; wild polio and a vaccine-derived form.

Wild polio can be prevented with a three-dose oral vaccine that contains an altered live form of the polio virus.

Sometimes the virus reactivates inside the body and then gets into the environment through faeces.

Once it is in contact with the water supply, the polio virus reverts to its wild strain and is able to spread.

The CDC said it had probably been caused by a reduction in the number and quality of mass vaccination programmes.

Steven Stewart, spokesman for the CDC's National Immunisation Programme, said: "In certain parts of the country, the vaccinators just didn't reach all the kids they should have."

Dr Gro Harlem Brundtland, Director-General of the WHO, said they would beat polio.

She said: "We have the tools and we have the strategies to finish this job."