One was confirmed on the island of Sumatra, which until last week was considered polio-free, said Oliver Rosenbauer, spokesman for the World Health Organization's polio eradication program in Geneva.

The other cases were all found in the provinces of Banten, West Java and the capital, Jakarta -- areas that already are undergoing large-scale immunization campaigns.

Dr. Bardan Jung Rana, a WHO medical officer in Indonesia, said the rise was not unexpected.

Most of the children affected "showed the onset of paralysis" before vaccinations began, he said, adding that patients need several doses of the vaccine before immunity is built up.

Likely Imported from Nigeria

Indonesia saw its first polio case since 1995 in April.

Health experts say the disease was likely imported from Nigeria, where polio vaccinations were suspended for several months in 2003 after radical Islamic preachers warned parents not to vaccinate their children because they believed it was part of a US plot against Muslims.

An emergency campaign to curb the disease involved vaccinating about 6.5 million children in West Java province, where the first case was found, and in the neighboring provinces of Jakarta and Banten.

A second round of vaccinations was completed on June 29 in the same three provinces, three days after a similar, separate campaign targeting 78,000 children under age 5 in Central Java.

Another immunization drive is scheduled nationwide and will include many of the same provinces.

Still Endemic in Six Countries

Rana, the WHO medical officer, said the number of polio cases in Indonesia is likely to continue to climb in coming weeks.

Children "are still not fully protected" and need more vaccinations, he said.

Polio is spread when unvaccinated people come into contact with the feces of those with the virus, often through water. It usually attacks the nervous system, causing paralysis, muscular atrophy, deformation and sometimes death, although only about one in 200 of those infected ever develop symptoms.

The disease is still endemic in six countries: Nigeria, India, Pakistan, Niger, Afghanistan and Egypt.