The Checkup

Genes may explain apparent link between narcolepsy and flu vaccine

Tuesday, February 15, 2011

Genes may explain apparent link between narcolepsy and flu vaccine

Scientists may have found a clue to explain a possible increased risk for narcolepsy among some people who got the H1N1 flu vaccine. According to the World Health Organization, excess cases of narcolepsy appear to have occurred among people with a gene that increases the risk for the rare disorder, which causes people to suddenly fall asleep.

Cases of narcolepsy have been reported in 12 countries among children and adolescents who received the swine flu vaccine in 2009. Sweden and Finland reported the most cases, with 60 of them in the latter country.

On Feb. 1, Finland's National Institute of Health and Welfare issued the results of an analysis of all new narcolepsy cases reported between 2006 and 2010 among those born after 1990. The analysis found an increased risk of narcolepsy among those ages 4 to 19 who received the Pandemrix H1N1 vaccine made by GlaxoSmithKline. The risk was about nine times higher for those who got the vaccine than for those of similar age who did not get vaccinated. That corresponds to a risk of about one case out of every 12,000 people in that age group vaccinated, officials estimated. Those ages 5 to 15 appeared to have the greatest risk. Of 22 Finnish cases tested so far, all were carrying a gene known to increase the risk for narcolepsy, the WHO said.

"The National Institute considers it probable that the Pandemrix vaccine was a contributing factor to this observed increase, and has called for further investigation of other co-factors that may be associated with the increased risk," the WHO said. "They consider it most likely that the Pandemrix vaccine increased the risk of narcolepsy in a joint effect in those genetically disposed with some other, still unknown, genetic and/or environmental factor."

- Rob Stein

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