GSK initially became aware of possible cases of narcolepsy following vaccination with the adjuvanted H1N1 pandemic vaccine Pandemrix through adverse event reports received by the Swedish Medical Products Agency, and subsequently via media reports in Finland.

Information on the individual cases remains limited at present, but GSK is conducting its own investigation in an effort to gather as much additional data as possible regarding the reported cases, and is working closely with key regulatory authorities, including the European Medicines Agency (EMA).

GSK has also proactively contacted the regulatory authorities in other countries where Pandemrix was used extensively. The cases reported as of 1500h GMT on 2 September 2010 have been primarily, but not exclusively, in Finland and Sweden, with a small number of additional cases reported in France. Media coverage has suggested small numbers of cases in Norway and Germany, but as of today GSK has received no reports from these countries.

To date, over 30 million doses of Pandemrix have been administered throughout Europe, with the most recent EMA Pharmacovigilance Report (19 August 2010) concluding that the benefit-risk profile of the three centrally-approved H1N1 vaccines, including Pandemrix, continues to be positive.

GSK's adjuvanted H1N1 pandemic vaccine, Arepanrix, manufactured in Quebec, was used extensively in Canada, with approximately 16 million doses administered. There are no reports of narcolepsy in Arepanrix recipients to date. However, given the background incidence of narcolepsy we cannot rule out the possibility of a small number of cases being reported in the future.

Narcolepsy is a chronic sleep disorder characterised by overwhelming daytime drowsiness and sudden sleep onset. The precise cause of narcolepsy is unknown, but there is growing evidence for either a genetic or environmental basis to the condition.

Global experience with previous large-scale immunisation programmes has shown that it is likely that a certain level of adverse events will be reported. The adverse events that are reported may be the result of underlying conditions, or new conditions that occur in temporal association with the vaccination, and some events may be related to the vaccine.

Having reviewed the currently available data and information regarding the reported cases of narcolepsy, which continues to remain limited, as well as GSK's own safety database, the Company has concluded that the currently available information is insufficient to assess the likelihood of a causal relationship between Pandemrix and narcolepsy.

Source: GlaxoSmithKline