Guillain-Barré syndrome has been a focus of safety monitoring since the report in 1976 of an increased risk of almost one extra case per 100 000 influenza vaccinations of swine origin.1 Subsequent studies have shown either no increased risk or a slightly increased risk (1-2 per million vaccinees) after vaccination for seasonal flu.2 The spread of the 2009 pandemic influenza A (H1N1) virus, which contained genes of swine origin, resulted in the development and widespread use of influenza A (H1N1) monovalent vaccines (2009 H1N1 vaccines).3 These included formulations containing oil in water adjuvants that had not previously been widely used in flu vaccines in Europe. Although available evidence suggested that the adjuvanted vaccines had acceptable safety profiles,3 data on the risk of rare adverse events, such as Guillain-Barré syndrome, were limited.

In the linked study (doi:10.1136/bmj.d3908), Dieleman and colleagues report the first data on adjuvanted 2009 H1N1 vaccines and the risk of Guillain-Barré syndrome from a …