The U.S. Centers for Disease Control and Prevention (news - web sites) (CDC) said 1,920 confirmed cases of polio were reported by laboratories in 2002, up from 483 the previous year. The agency attributed most of the rise to a large outbreak in India, one of seven countries where the virus is still endemic.

Polio, which once afflicted millions of children, attacks the central nervous system, often causing paralysis, muscular wasting and deformity. Five to 10 percent of those infected die when their breathing muscles become paralyzed.

The scourge, usually contracted by children through exposure to contaminated water, largely disappeared from the Western world as a result of vaccination programs begun in the 1950s, but still exists in a few Asian and African nations.

Nigeria, Egypt, Somalia, Niger, Pakistan and Afghanistan (news - web sites) also reported polio cases in 2002.

The battle against polio hit its biggest roadblock last year in the Indian states of Uttar Pradesh and Bihar, which reported the worst outbreaks since 1988, when the World Health Organization (news - web sites) (WHO) embarked on a major eradication program.

The two states, among the poorest in India, accounted for 1,362, or 71 percent, of the world's cases in 2002. A reduction in the number and quality of mass vaccination programs likely caused the epidemic, the CDC said.

"In certain parts of the country, the vaccinators just didn't reach all the kids they should have," said Steven Stewart, a spokesman with the CDC's National Immunization Program.

Mass vaccination campaigns have been the linchpin of global efforts to stamp out the wild form of the polio virus, as well as prevent the spread of its vaccine-derived form.

Wild polio can be prevented with a three-dose oral vaccine that contains an altered live form of the polio virus. In rare cases, the virus can reactivate inside a vaccinated person and escape into the environment through feces.

Once in contact with the water supply, the virus then reverts to its wild strain and is free to spread to others who have not been immunized, as occurred during a deadly outbreak in 2000 and 2001 in Haiti and the Dominican Republic.

Fears that this could occur in India prompted the WHO and Indian authorities earlier this month to launch a major vaccination campaign to inoculate an estimated 80 million children in six Indian states. A number of follow-up vaccination campaigns are planned in the next year.

Although the outbreaks in India offered a sobering snapshot of the difficulties faced in stamping out polio, there were still signs last year that the overall war against the disease was being won.

Ethiopia, Sudan and Angola -- three countries where the virus had been endemic -- were declared polio-free in 2002, and vaccinators' access to children in Somalia and Afghanistan also improved considerably, according to the CDC.

The WHO hopes to completely wipe out polio by 2005.

"We have the tools and we have the strategies to finish this job," WHO Director-General Dr. Gro Harlem Brundtland said earlier this month.