Pandemrix™ and narcolepsy: A critical appraisal of the observational studies.

A link between Pandemrix™ (AS03-adjuvanted H1N1 pandemic influenza vaccine, GSK Vaccines, Belgium) and narcolepsy was first suspected in 2010 in Sweden and Finland following a number of reports in children and adolescents. Initial scepticism about the reported association faded as additional countries reported similar findings, leading several regulatory authorities to restrict the use of Pandemrix™. The authors acknowledge that currently available data suggest an increased risk of narcolepsy following vaccination with Pandemrix™; however, from an epidemiologist's perspective, significant methodological limitations of the studies have not been fully addressed and raise questions about the reported risk estimates. We review the most important biases and confounders that potentially occurred in 12 European studies of the observed association between Pandemrix™ and narcolepsy, and call for further analyses and debate.