The European Medicines Agency (EMA) has launched a review of GlaxoSmithKline’s pandemic influenza vaccine Pandemrix to investigate whether there is a link between vaccination and cases of narcolepsy, a rare sleep disorder. The vaccine has been used for vaccination against H1N1 influenza in more than 30 million Europeans since September 2009; however, the EMA stresses in a statement that only a small number of narcolepsy cases have been reported and it is not yet known if the vaccine caused the disorder. Narcolepsy causes a person to fall asleep suddenly and unexpectedly, and its precise cause is unknown.

“The Agency’s Committee for Medicinal Products for Human Use (CHMP) will look carefully at all of the available data to determine whether there is any evidence for a casual association,” said the EMA statement. “As part of this evaluation, the Committee will also consider the so-called background rate for narcolepsy, i.e. the number of cases that would normally be expected to be diagnosed.”

The narcolepsy cases that may possibly be linked to the vaccine were all collected through spontaneous reporting systems, mainly in Sweden in Finland. In particular, Finland observed a rise in narcolepsy cases among children and adolescents, and the Finnish National Institute for Health and Welfare (THL) recommended last week that use of the vaccine be discontinued in Finland until an explanation is found.

“A number of different reasons may be behind the observed rise in the incidence of narcolepsy: A(H1N1) infection, vaccination, a compound effect of infection and vaccination, or some other factor entirely. Infections in general are known to cause narcolepsy,” said a statement from the THL.

According to the EMA, its CHMP will be working with experts across the EU to assess Pandemrix and any potential changes to the vaccine’s benefit/risk balance. The CHMP will also consider the need for any provisional measures at its September 2010 meeting. In Finland, THL experts and pediatric neurologists will also be investigating the matter. The THL has said that it will relay any research results abroad for use in other countries’ vaccination programs.