The World Health Organisation (WHO) said more investigation was needed into the possible risk of narcolepsy, a rare sleeping disorder, from GlaxoSmithKline's Pandemrix H1N1 flu vaccine.

A WHO advisory panel made the decision after a Finnish study published last week suggested children who got the shot were nine times more likely to suffer from narcolepsy, which causes a person to fall asleep suddenly and unexpectedly.

WHO spokeswoman Alison Brunier told a briefing in Geneva that Pandemrix remains on the WHO's list of prequalified vaccines, and there would be no changes to WHO recommendations as a result of the Finnish study.

"This means that countries should continue vaccinating against H1N1 to immunise people at risk of severe disease ...using monovalent vaccines, including Pandemrix, if no trivalent seasonal vaccine is available," she said.   

A spokesman for the British drugmaker said it had been expecting the WHO statement and was itself looking into reports of links between narcolepsy and Pandemrix.   

"GSK is reviewing the Finnish report and believes it would be premature to draw any conclusions," he said in a statement.   

Pandemrix was designed to tackle the H1N1 pandemic flu which spread around the world in 2009 and 2010.    

It is not currently being widely used, as the pandemic was declared over in August last year, but doctors in some countries, such as Britain, have been advised to use it if their stocks of seasonal flu vaccines run low.   

The United Nations health body said an increased risk of narcolepsy had not been seen in association with the use of any other vaccines, either against flu or other diseases.    

"At this stage, it does not appear that narcolepsy following vaccination against pandemic influenza is a general worldwide phenomenon and this complicates interpretation of the findings in Finland," the WHO's advisory panel said in a statement.

It said the Stockholm-based European Centre for Disease Prevention and Control (ECDC), which monitors disease in the European Union (EU), is currently conducting studies of narcolepsy and pandemic flu vaccines. -Reuters