The narcolepsy-pandemic influenza story: can the truth ever be unraveled?

A safety signal around Pandemrix, an AS03 adjuvanted influenza A(H1N1) pdm09 vaccine potentially causing narcolepsy in children and adolescents became public in August 2010, long after cessation of the influenza A(H1N1) pdm09 campaigns in Europe. The signal originated from Finland and Sweden, two countries with school based pandemic vaccination campaigns, with high vaccine coverage, and vaccinations being provided at the peak of the circulating wild virus. Since the announcement awareness grew in Europe, with extensive public media dissemination and regulatory actions. This resulted in a steep increase in the spontaneous reports of exposed cases, a decrease in diagnostic lag times of this rare, underdiagnosed disease and finally victim compensation. The signaling countries conducted rapid risk assessment studies to quantify the signal to the best of their abilities, in the midst of the public awareness, most of which could not distinguish between a vaccine and an awareness effect. Due to the strong but variable associations from the epidemiological studies, the search for biological mechanisms started. Currently it is not yet understood how Pandemrix might cause narcolepsy, and whether it would be specific to Pandemrix. The paper describes the current evidence and puts forward the questions that remain to be answered, which are relevant for future pandemic preparedness when adjuvants may be used for dose sparing.