The World Health Organization is reviewing the safety of GlaxoSmithKline's Pandemrix H1N1 flu vaccine after a Finnish study suggested children who got the shot were nine times more likely to suffer from narcolepsy, a rare sleeping disorder.
Narcolepsy causes a person to fall asleep suddenly and unexpectedly. Its precise cause is unknown but it is generally considered to be triggered by a combination of genetic and environmental factors.
Researchers at Finland's National Institute for Health and Welfare (NIHW) said Tuesday their research suggested it was "most likely" the increase they found in narcolepsy was a joint effect of Pandemrix and some other factor or factors.
Their research, which was described as preliminary, was conducted by the Finnish national narcolepsy committee and published by the NIHW, found an increase in cases of narcolepsy among children aged four to 19 years who had the vaccine.
GSK said it was aware of the research but believed it was too soon to draw any conclusions. A separate investigation by European drugs regulators is already underway.
The Geneva-based WHO said in a statement that further investigation was required "concerning narcolepsy and Pandemrix vaccine" and it was working on this.
"WHO's Global Advisory Committee on Vaccine Safety (GACVS) is considering all available data relating to reports of increased rates of narcolepsy and is expected to issue a statement on its website within the coming days," it said.
Recommendations for the use of seasonal flu vaccines for 2010/2011 remain unchanged, it said, the issue of narcolepsy had not been linked with any other H1N1 pandemic flu vaccines, seasonal flu vaccines or any other adjuvanted, or boosted, vaccines used in childhood immunization programs.
GSK said it was reviewing the report and "it would be premature to draw any conclusions on a potential association between Pandemrix and narcolepsy until this European investigation has been completed."
Hanna Nohynek, the NIHW's vaccine safety officer, said the baseline risk for narcolepsy in children aged four to 19 was less than 1 per 100,000, and the study found that among those who had the Pandemrix shot the risk rose to 8.1 per 100,000.
According to GSK, more than 31 million doses of Pandemrix have been administered worldwide in 47 countries. The company said it had received reports of a total of 162 cases of narcolepsy as of January 31, 2011, with 70 percent of these cases of narcolepsy originating from Finland and Sweden.
The EMA, which regulates and reviews the safety of drugs in the European Union, said in September it was reviewing Pandemrix after reports of a link between the vaccine and narcolepsy, but there was no evidence yet to confirm a link. An EMA spokeswoman said the safety review was continuing. "For the time being ... the benefit-risk balance of Pandemrix remains positive," she said.
The Finnish report said that during 2009 and 2010, 60 children and adolescents aged four to 19 years fell ill in Finland with narcolepsy. Of those who fell ill, 52, or almost 90 percent, had received Pandemrix, it said, and the vaccine coverage in the entire age group was 70 percent.
The Finnish institute said it would seek to confirm its findings in further investigations by August 2011.
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