Study Again Finds Narcolepsy Risk With H1N1 Flu Vaccine

Megan Brooks

March 01, 2013

A study from England shows a significant 14-fold increased risk for narcolepsy in children vaccinated with AS03 adjuvanted pandemic A/H1N1 2009 influenza vaccine (Pandemrix, GlaxoSmithKline) during the pandemic.

The study points to a "causal association" consistent with findings from Finland and Sweden, Elizabeth Miller, consultant epidemiologist, Health Protection Agency, Colindale, London, United Kingdom, and colleagues reported online February 26 in the British Medical Journal.

The researchers emphasize that the risk might be overestimated by more rapid referral of vaccinated children, and they call for long-term follow-up of children who received the vaccine to get a better handle on the exact level of risk.

Interpret Cautiously

Pandemrix was introduced in Europe in October 2009 during the second wave of infection, initially for people with high-risk clinical conditions and then in healthy children. By March 2010, around 1 in 4 (24%) healthy children younger than age 5 years and just over a third (37%) aged 2 to 15 years in a risk group had been vaccinated. v

Altogether, more than 30 million doses of the vaccine were administered in European countries during the H1N1 flu pandemic. It was not used in the United States.

In August 2010, concerns were raised in Finland and Sweden about a possible association between narcolepsy and this vaccine.

A 2012 study from Finland reported a 13-fold increased risk for narcolepsy in children and young people aged 4 to 19 years who got the vaccine. Most of those who developed narcolepsy had onset within 3 months of vaccination, and all did so within 6 months of vaccination.

However, in October 2012, a review of the evidence  by the European Medicines Agency (EMA)'s Committee on Human Medicinal Products (CHMP) concluded the evidence was not sufficient to confirm a link between the vaccine and narcolepsy cases.

"After careful consideration, the CHMP concluded that the data presented by the Finnish researchers are preliminary and that the evidence presented so far is insufficient to allow conclusions to be drawn, and does not lead to any new concerns regarding Pandemrixor other vaccines, including other influenza vaccines," an EMA statement noted. "On the basis of the current evidence, the role of the Pandemrix antigen and its adjuvant on the association between Pandemrix and narcolepsy remains unknown."

To evaluate the risk for narcolepsy afterPandemrixvaccination in England, Miller and colleagues reviewed the medical records of 245 children and adolescents aged 4 to 18 years seen at sleep and child neurology centers across England.

From this group, they identified 75 children with narcolepsy (56 with cataplexy) with onset after January 1, 2008. Eleven had received the vaccine before their symptoms started, and  7 had received it within 6 months of vaccination.

In children with a narcolepsy diagnosis by July 2011, the odds ratios were 14.4 (95% confidence interval [CI], 4.3 -  48.5) for vaccination at any time before onset and 16.2 (95% CI, 3.1 - 84.5) for vaccination within 6 months before onset, the researchers say.

In a self-controlled case series analysis, the relative incidence in those with a diagnosis by July 2011 with onset from October 2008 to December 2010 was 9.9 (95% CI, 2.1 - 47.9).

In absolute terms, the researchers calculated that 1 in 52,000 to 57,500 doses of Pandemrixare associated with narcolepsy.

This study shows that the increased risk for onset of narcolepsy in children and young people after Pandemrixvaccination is not confined to Scandinavian populations, the researchers say.

"The magnitude of the increased risk found in English children and young people is similar to that reported from Finland," they write.

Although further use of this vaccine for prevention of seasonal flu "seems unlikely," they say their findings "have implications for the future licensure and use of AS03 adjuvanted pandemic vaccines containing different subtypes such as H5 or H9."

"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 researchers conclude.

The study was funded by the Department of Health policy research program and the Health Protection Agency.  The authors have disclosed no relevant financial relationships.

BMJ. 2013;346:f794. Full text