In addition to the data from Finland, research is ongoing in Sweden where there has also been an unexpected number of narcolepsy reports following vaccination with Pandemrix. However, other non-Nordic countries have not seen similar increased rates of reporting of narcolepsy. 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. Therefore, at present definitive conclusions cannot be drawn and no changes to the recommendations for use of Pandemrix are proposed.
The Committee reviewed the preliminary results of the Finnish study, an epidemiological study that compared the incidence of narcolepsy in people aged 4 to 19 years vaccinated with Pandemrix between 1 January 2009 and 31 December 2010 with the incidence of narcolepsy in unvaccinated people of the same age. The study, conducted by the Finnish National Institute for Health and Welfare (THL), suggested a nine-fold increase in risk of narcolepsy in the vaccinated population studied (an increase from approximately 1 to 9 cases per 100,000 vaccinees), although the occurrence of narcolepsy was still very rare even with this apparent increase.
The Committee concluded that the THL study was well-designed, although it remains possible that unmeasured effects and biases could potentially have contributed to the observed increased risk. 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.
In order to conclude this review the CHMP considers it important to gather more data from the use of Pandemrix and related vaccines in a variety of countries to further assess this concern, and thereby understand the nature of any relationship between vaccination and narcolepsy. A variety of research efforts are now ongoing, including an epidemiological study of narcolepsy and pandemic vaccines conducted by the European Centre for Disease Control and Prevention (ECDC) through a network of research and public health institutions (VAESCO) in nine European Union Member States. The final results of this study are expected by the end of June 2011.