By Lucy Piper, Senior medwireNews Reporter
Researchers have found an increased risk for narcolepsy in children who received the swine flu vaccination in England.
The team estimates that one in 52,000 to 57,500 doses of the vaccine, AS03 adjuvanted pandemic A/H1N1 2009, which was introduced in October 2009, is associated with the development of narcolepsy.
The finding, published in the BMJ, confirms the results of a previous study from Finland, and dispels speculation that the association may be restricted to Scandinavian populations.
"The increased risk of narcolepsy after vaccination with ASO3 adjuvanted pandemic A/H1N1 2009 vaccine indicates a causal association, consistent with findings from Finland. Because of variable delay in diagnosis, however, the risk might be overestimated by more rapid referral of vaccinated children," Elizabeth Miller (Health Protection Agency, London, UK) said in a press statement.
"Long-term follow up of people exposed to [ASO3 adjuvanted pandemic A/H1N1 2009] is needed before we can fully establish the extent of the association."
The researchers reviewed the medical notes of 75 children and adolescents aged 4-18 years attending sleep centers and child neurology centers across England, who had been diagnosed with narcolepsy from January 2008. Of these, 11 had been vaccinated with AS03 adjuvanted pandemic A/H1N1 2009 before the onset of symptoms.
After adjusting for clinical conditions for which flu vaccination is recommended, the vaccine was associated with a 14.4-fold increased risk for narcolepsy. The risk was even higher for the seven children who had been vaccinated within 6 months of symptom onset, at 16.2-fold.
Study co-author John Shneerson, from Papworth Hospital in Cambridge, UK, suggested to the press: "[The vaccine] may have triggered an immune reaction against the sleep centre cells in those children who were genetically predisposed to develop narcolepsy."
Although further use of the vaccine for the prevention of seasonal A/H1N1 2009 is unlikely, following changes by the European Medicines Agency to its indication for use, the researchers note that its license is still valid and that the vaccine can still be made and sold in Europe.
"Further studies to assess the risk, if any, associated with the other A/H1N1 2009 vaccines used in the pandemic, including those with and without adjuvants, are also needed to inform the use of such vaccines in the event of a future pandemic," the team concludes.
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