WHO probes into swine flu narcolepsy cases

The WHO said that such sleep disorders, mainly in youngsters, had not been seen with vaccines in the past, and were more frequent in Sweden, Finland and Iceland than in other countries.

However, the UN health agency decided to keep its advice in favour of vaccination, including with the Pandemrix vaccine highlighted in the study, because it still felt the benefits outweighed a relatively small risk, spokeswoman Alison Brunier said.

Narcolepsy is a sleep disorder which causes extreme fatigue and often results in the patient falling soundly asleep without warning, even in the middle of an activity.

According to WHO, the Pandemrix vaccine made by GlaxoSmithKline was used in 47 countries worldwide during 2009-2010 and was included by the agency in donations made to poor nations during the flu pandemic.

The WHO Global Advisory Committee on Vaccine Safety (GACVS) last week reviewed data from a Finnish study, which found that children injected with the Pandemrix flu vaccine were nine times more likely to contract narcolepsy than those who were not vaccinated.

"The committee agrees that further investigation is warranted concerning narcolepsy and vaccination against influenza (H1N1) 2009 with Pandemrix and other pandemic H1N1 vaccines," the WHO said. "An increased risk of narcolepsy has not been observed in association with the use of any vaccines whether against influenza or other diseases in the past," it added.

"Since August 2010, following widespread use of vaccines against influenza (H1N1) 2009, cases of narcolepsy, especially in children and adolescents, have been reported from at least 12 countries," WHO said.

However Brunier said there is no change to the UN health agency current position on use of pandemic influenza vaccines. "This means that countries should continue vaccinating against H1N1 to immunise persons at risk of severe disease, using monovalent vaccines including Pandemrix if there is no trivalent seasonal vaccine available," she said.