The UN health agency was advising Saudi Arabia ahead of the upcoming Hajj pilgrimage and knew no more cases in the Gulf of a mystery illness from the same virus family as the deadly SARS.
"WHO is working closely with the Kingdom of Saudi Arabia, as in previous years, to support the country's health measures for all visitors participating in the hajj pilgrimage to Mecca next month," the World Health Organization said in a statement.
The Geneva-based agency earlier confirmed that the illness was in the coronavirus family and had caused the death of a Saudi national.
It has also left a Qatari man seriously ill in a London hospital after he was transferred there from Doha earlier this month, the WHO said, adding that he had previously been in Saudi Arabia.
The two cases occurred three months apart in June and September, said the WHO, stressing that the illness is not Severe Acute Respiratory Syndrome which swept out of China in 2003, killing more than 800 people worldwide.
What sets the new virus apart from SARS, the agency added, is that it causes rapid kidney failure.
Meanwhile, pilgrims have already begun to arrive in the Saudi kingdom for the ritual that represents the world's largest annual gathering.
Last year, nearly three million Muslim pilgrims performed the Hajj, which represents one of the five pillars of Islam and must be performed at least once in a lifetime by all Muslims who are able to do so.
Saudi health authorities have downplayed the chances of an outbreak of the mystery illness, adding that there were no changes on travel conditions for pilgrims.
Meanwhile a Danish hospital said Wednesday it had isolated five people with symptoms of a viral respiratory illness pending the result of tests.
Odense University hospital said those admitted were a family of four where the father had been to Saudi Arabia, and an unrelated person who had been to Qatar.
Two of the patients were children under five.
SARS swept out of China in 2003, killing more than 800 people worldwide.