A campaign to halt the spread of polio by year-end is on track despite a new case in Saudi Arabia that sparked fears it could be carried by Muslims going home after the Haj, the World Health Organisation said on Friday.

A Nigerian boy living in Mecca, Islam’s holy city, came down with the disease in mid-December despite being vaccinated, but has recovered from temporary paralysis, WHO officials said.

He was believed to have caught the crippling virus from visitors from Nigeria, epicentre of Africa’s polio outbreak, in what was the third case “imported” into the kingdom from Nigeria or Sudan since September.

“It is not a major setback to the initiative,” Bruce Aylward, coordinator of the WHO’s global polio eradication initiative, told a news briefing. “The stars have started to line up very, very favourably in terms of getting it finished.”

The United Nations agency is waging a campaign to stop the transmission of polio by the end of 2005, but the number of new cases rose 50 percent worldwide to 1,185 last year, largely because of the continuing spread in Nigeria.

Polio, which mainly affects children under the age of five, is carried by a virus and can cause irreversible total paralysis in a matter of hours.

More than 2.5 million Muslims travelled to Mecca to attend the annual pilgrimage, which ended in late January. More than 95 percent of Saudi children are immunised, according to the WHO.

“What (the case in) Saudi Arabia reminds us is that we have to get the vaccine into every kid right across west and central Africa. This is the low season, the Achilles heel of the virus,” Aylward said.

In tropical areas, now in a dry period, it is the low season for transmission, ideal to try to stamp out the virus, he said.

Government commitment was also strong ahead of a campaign to immunise 80 million children in 18 west and central African countries in late February.

Africa’s polio epidemic was caused by a 10-month halt in immunisation in the northern Nigerian state of Kano where Muslim elders said the vaccines were part of a Western plot to spread HIV and infertility, according to WHO officials. Nigeria, which resumed immunisation last July, had 763 cases in 2004.