Why flu vaccine may cause narcolepsy
Scientists think they have found a clue to why there may be an increased risk for the sleeping disorder narcolepsy among some people who got the H1N1 flu vaccine: The cases appear to have occurred among those carrying a gene that increases the risk for the rare disorder, which causes people to suddenly fall asleep, according to the World Health Organization.
Cases of narcolepsy have been reported among children and adolescents who received the vaccine during the swine flu epidemic in 2009 in 12 countries, with Sweden and Finland reporting the most cases. A total of 60 cases were reported in Finland.
On Feb. 1, Finland's National Institute of Health and Welfare reported 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 Pandemerix H1N1 vaccine made by GlaxoSmithKline. The risk was about nine times higher among those who got the vaccine, corresponding 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 of the cases in Finland tested so far, all were carrying a gene known to increase the risk for the condition, the WHO announced Tuesday.
"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."
The WHO's Global Advisory Committee on Vaccine Safety reviewed the Finnish data Feb. 4 and "agrees that further investigation is warranted," according to the statement.
"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 noted. "Even 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 European Centre for Disease Prevention and Control is conducting epidemiological studies of narcolepsy and pandemic influenza vaccines, the WHO said.
"The findings from these studies and others, including further investigations in Finland, may help clarify the determinants of any increased risk of narcolepsy which currently appears to be restricted to the months following vaccination and by age group and country," the statement said.
| February 8, 2011; 9:46 AM ET
Categories: Influenza, Parenting, Sleep, Vaccinations
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