HELSINKI/LONDON (Reuters) - GlaxoSmithKline Plc's H1N1 pandemic flu shot may put adults at higher risk of developing narcolepsy, not only children as previous studies found, Finland's National Institute for Health and Welfare said on Thursday.
Growing evidence of a link between GSK's Pandemrix vaccine and an increase in narcolepsy, a rare sleep disorder, among children who received it in Europe has delayed approval of a similar vaccine in the United States.
Data published this year in the British Medical Journal found that children in England who had been vaccinated with Pandemrix during the 2009-10 H1N1 swine flu pandemic had a 14-fold higher risk of developing narcolepsy, equating to about one in 50,000.
Finland's National Institute said an analysis of hospital and primary care data in Finland found that people aged between 20 and 64 who had been vaccinated with Pandemrix were 3 to 5 times more likely to develop narcolepsy than unvaccinated people.
Narcolepsy is a lifelong, incurable and potentially debilitating sleep disorder that can cause hallucinations, bouts of daytime sleepiness and cataplexies - where strong emotions trigger a sudden loss of all muscle strength.
Previous studies in Finland, Sweden and Ireland have also found a link between Pandemrix and narcolepsy, and GSK says more than 800 cases linked to the shot have been reported in Europe.
The British drugmaker says some 30 million doses of the vaccine were administered across Europe during the 2009-10 H1N1 pandemic. The pandemic was declared over in August 2010.
The company acknowledges an association but says there is as yet insufficient evidence to show that Pandemrix is the cause.
Reporting by Ritsuko Ando in Helsinki and Kate Kelland in London; Editing by Kevin Liffey