Four young children in Indonesia are now confirmed to have polio, a disease which has no cure, in the country's first outbreak in a decade.
Health Officials are still investigating other suspected cases which have been reported in the same area of a West Javanese province.
The World Health Organization (WHO) has called on Indonesia which has a good record of vaccination coverage, to accelerate its campaign.
The WHO said on Thursday that two more infants were confirmed to have the disease, following an announcement by Indonesian authorities earlier this week that two other children were infected.
An initiative has now been launched by authorities to immunise five million children in the area, they say they are confident they can prevent a major outbreak.
Polio is a waterborne disease which usually infects young children by attacking the nervous system. It causes paralysis and muscular atrophy, and there is no cure.
Polio vaccination rates across Indonesia as a whole stand at about 90%, but in western Java the rate has been around 55%.
DNA tests done on a viral sample from one of the infected children has shown that the polio arrived in Indonesia from Nigeria, via Saudi Arabia, and experts suspect the strain could have been carried by migrant workers or pilgrims visiting Muslim holy sites in Saudi Arabia.
The disease which has practically disappeared in the developed world is still endemic in Nigeria, a problem exacerbated in 2003 when Muslim clerics there spread fear with rumours that the polio vaccine had been contaminated to make Muslims infertile, supposedly as part of a US plot to undermine the spread of Islam.
The international campaign for universal vaccination against polio has been one of the great successes in the global fight against disease of recent years. Polio was endemic across the world until the middle of last century, when a vaccine was discovered.