Indonesian authorities have reported 11 new cases of polio after a house-to-house search for paralysed children, pushing the total in the two-month outbreak to 111, the World Health Organisation (WHO) said on Wednesday.

The newest cases all occurred in the province of Banten on the island of Java, the epicentre of the outbreak, said WHO polio spokesman Oliver Rosenbauer, and indicate that disease may have hit harder than authorities thought previously.

“The virus has spread,” Rosenbauer said. “What really needs to happen is that the immunisation response needs to be intensified further.”

Polio, which can cause irreversible paralysis in hours, reemerged in May in Indonesia, which was polio-free since 1995.

The WHO warned the outbreak may continue to spread and that circulation of the wild polio virus could be occurring in additional provinces.

Particularly alarming is that the virus has now spread beyond Java and has hit the neighbouring island of Sumatra, Rosenbauer said.

“It’s a very large outbreak,” he said. “It’s very serious in Sumatra because the virus has spread, it has jumped to another island.”

A fresh round of immunisation was carried out last week, targeting 6.4 million Indonesian children under the age of five in West Java, Banten and Jakarta provinces.