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New findings on H1N1 vaccine prompt revised prescribing advice

BMJ 2011; 342 doi: https://doi.org/10.1136/bmj.d2524 (Published 18 April 2011) Cite this as: BMJ 2011;342:d2524
  1. Geoff Watts
  1. 1London

New findings on the suspected link between the H1N1 vaccine Pandemrix and narcolepsy in children and adolescents have prompted the European Medicines Agency to recommend interim changes to its product information.

The findings in question are the preliminary results of a Swedish registry study of a group of children and adolescents aged under 20 years who received Pandemrix between October 2009 and December 2010. The number of cases of narcolepsy in this group was four times the number in an unvaccinated group of the same age (4.1 cases per 100 000 person years versus 0.97 cases per 100 000 person years (relative risk 4.2 (95% confidence interval 1.8 to 12.1)).

This difference is broadly in line with the findings of an earlier study from Finland.

The agency’s Committee for Medicinal Products for Human Use, the body responsible for assessing the new data, said that the Swedish study had some inherent limitations but had been well conducted.

It said, “The lack of a clear increase in reports of narcolepsy following Pandemrix in other EU [European Union] and non-EU countries may point towards the influence of other unknown factors affecting the trend seen in some countries,” it said. It added that there is currently no plausible biological explanation for the association and that further non-clinical studies will be needed.

In addition to providing prescribers with the new epidemiological data, the amended product information will say, “When considering the use of Pandemrix in children and adolescents, an individual benefit risk assessment should be performed taking this information into account.”

The committee describes its ruling as an interim measure pending the outcome of a European review of Pandemrix expected to conclude in July 2011. It also plans to hold a meeting with international experts, the World Health Organization, and the European Centre for Disease Prevention and Control.

In a statement issued on 15 April GlaxoSmithKline, the manufacturer of Pandemrix, said, “GSK maintains that further information must be gathered on a potential likelihood of a causal relationship between Pandemrix and narcolepsy before any conclusions can be drawn.

“It is important to wait for the results of the ongoing European investigation, which includes an epidemiological study of narcolepsy and pandemic vaccines across a network of research and public health institutions . . . in nine European Union member states.”

Narcolepsy occurs naturally at an annual rate of around one case in every 100 000 people. Although its precise cause is unknown, it is generally thought to be triggered by a combination of genetic and environmental factors.

Notes

Cite this as: BMJ 2011;342:d2524

Footnotes

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