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Higher risk of narcolepsy in children who had swine flu vaccine

Vaccinated children 14 times more likely to have sleep disorder

Adrian O'Dowd

Wednesday, 27 February 2013

UK children given the swine flu vaccine Pandemrix in 2009-10 are 14 times more likely to have narcolepsy than other children, according to a study published online today in the BMJ.

A team of UK researchers who identified the higher prevalence of the sleep disorder have, however, called for further research, saying the risk may be overestimated by more rapid referral of vaccinated children.

In 2009, pandemic influenza A/H1N1 virus spread rapidly, resulting in millions of cases and over 18,000 deaths in over 200 countries.

In England the vaccine Pandemrix was introduced in October 2009 and by March 2010, around one in four (24%) of healthy children aged under 5 and just over a third (37%) aged 2-15 in a risk group had been vaccinated.

In August 2010, concerns were raised in Finland and Sweden about a possible association between narcolepsy and Pandemrix. This was followed in 2012 by a study from Finland that reported a 13-fold increased risk in children and young people aged 4-19.

However, a lack of reported cases in other countries led to speculation that any possible association might be restricted to these Scandinavian populations.

A team of researchers from the Health Protection Agency, Addenbrooke’s Hospital and Papworth Hospital, both in Cambridge and University College London set out to evaluate the risk after vaccination in England.

They reviewed case notes for 245 children and young people aged 4-18 from sleep centres and child neurology centres across England.

Of these, 75 had narcolepsy (56 with cataplexy) with onset after 1 January 2008. Eleven had been vaccinated before onset of symptoms – seven within six months.

After taking clinical conditions into account, they found that vaccination at any time was associated with a 14-fold increased risk of narcolepsy, whereas vaccination within six months before onset was associated with a 16-fold increased risk.

In absolute numbers, this means that one in 52,000 to 57,500 doses are associated with narcolepsy, said the authors.

They stressed that the risk may be overestimated and called for longer term monitoring of the cohort of children and adolescents exposed to Pandemrix to evaluate the exact level of risk.

“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,” they said.

They concluded: “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.”

A Department of Health spokesman said: “The decision to recommend that children got this vaccine during the flu pandemic was based on evidence available at the time, along with the advice from the European Medicines Agency which approved its use.

“We keep all emerging evidence under review and that's why use of Pandemrix in those less than 20 years old was stopped in the UK in 2011.”

DOI: 10.1136/bmj.f794

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