The UK's largest drugmaker, GlaxoSmithKline, is investigating whether its H1N1 pandemic vaccine Pandemrix is responsible for inducing the sleep disorder narcolepsy.
GSK initially became aware of possible cases of narcolepsy following vaccination with Pandemrix through adverse event reports received by the Swedish Medical Products Agency, subsequently reported in the media reports in Finland.
So far, information on the individual cases is limited, but GSK says it is conducting its own investigation to gather as much additional data regarding the reported cases, and working with key regulatory authorities, including the European Medicines Agency (EMA).
GSK says it has also 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," GSK said in a statement.
Media coverage has suggested small numbers of cases in Norway and Germany, but GSK says it has, so far, not received any reports from these countries.