After reviewing further data on the suspected link between cases of narcolepsy and GlaxoSmithKline’s pandemic influenza vaccine, Pandemrix, the EMA’s Committee for Medicinal Products for Human Use (CHMP) is still unable to establish a causal relationship.

New evidence from a study in Finland has added to the concern by suggesting that there could be a nine-fold increase in the risk of narcolepsy in the vaccinated population, but the CHMP still believes that further analyses and study results are required, particularly as the risk does not appear to be a global phenomenon. According to the EMA, the majority of the narcolepsy cases have been reported in Finland and Sweden, but similar increased rates of narcolepsy have not been seen in other Nordic countries. “Additionally, in Canada, where there has been substantial use of this type of vaccine, there has been no evidence of an increase in reports of narcolepsy,” explained an EMA statement.

The EMA has been investigating the safety of Pandemrix since August 2010 and recently the World Health Organisation also issued a call for further investigation. The CHMP concluded that the study in Finland, conducted by the Finnish National Institute for Health and Welfare, was well designed, but unmeasured effects and biases could have contributed to the increased risks.

“One possible explanation for the results is that Pandemrix may have interacted with an unknown local environmental and/or genetic factor in contributing to an increased risk of narcolepsy among those aged 4 to 19 years in Finland,” said the EMA.

To further understand the concern, the CHMP says it is important to gather more data from the use of Pandemrix and related vaccines in a variety of countries. A number of studies are now underway, including an epidemiological study of narcolepsy and pandemic vaccines conducted by the European Centre for Disease Control and Prevention. The final results of this study are expected at the end of June 2011.

www.ema.europa.eu