Infection with influenza virus affects a substantial proportion of the worldwide population each year. In 2009, the perceived global threat of influenza reached an exceptional level after the emergence of a novel swine-origin influenza A H1N1 (so-called swine flu), which was first isolated in local outbreaks in Mexico, Canada, and the USA. The subsequent rapid global spread of this strain and concerns about its possible virulence led national and global health authorities to initiate countermeasures in early 2009, by means of mass immunisation programmes in several countries, including the USA and countries of the European Union. These vaccination campaigns were the cornerstone of public health measures to prevent the undesired consequences of a pandemic. They also served as a reminder (at least to the neurological community) of the 1976 national influenza immunisation programme against swine flu subtype A/NJ/76 in the USA, which was stopped because of the emergence of Guillain-Barré syndrome (GBS) in vaccine recipients.
GBS after vaccination is rare, and most studies have concluded that it is a chance event except in the 1976 programme. However, the small size of vaccine safety trials before licensing, the testing and licensing of vaccines for potential pandemic diseases before the start of the pandemic (so-called mock-up licensing), and the very low incidence of GBS mean that data could be insufficient to assess the risk reliably. Conventional vaccine safety monitoring after licensing does not entirely eradicate this concern.
By contrast with vaccination, evidence is increasing that influenza infection and influenza-like illnesses can act as triggers for GBS. This important fact, which has been highlighted in epidemiological studies, and seems to be underappreciated in public and professional advisory interpretations of influenza vaccine adverse event data and subsequent risk–benefit assessments. The establishment of background rates for GBS will be very useful in this regard; this information has already been provided for several countries.
In addition to the prevention of multiple non-neurological diseases by influenza vaccination, awareness and correct interpretation of all available data about the relation of GBS, influenza infection, and influenza vaccination are a prerequisite for an objective risk–benefit analysis of current and future influenza vaccination campaigns. This paper reviews the existing data derived from studies about GBS after influenza infection and GBS after exposure to influenza vaccine and summarises current information about the plausibility of influenza immunisation as a biological cause of GBS.
Guillain-Barré syndrome after exposure to influenza virus. Lancet Infectious Diseases (2010) 10(9) 643- 651 doi:10.1016/S1473-3099(10)70140-7
Guillain-Barré syndrome (GBS) is an acute, acquired, monophasic autoimmune disorder of peripheral nerves that develops in susceptible individuals after infection and, in rare cases, after immunisation. Exposure to influenza via infection or vaccination has been associated with GBS. We review the relation between GBS and these routes of exposure. Epidemiological studies have shown that, except for the 1976 US national immunisation programme against swine-origin influenza A H1N1 subtype A/NJ/76, influenza vaccine has probably not caused GBS or, if it has, rates have been extremely low (less than one case per million vaccine recipients). By contrast, influenza-like illnesses seem to be relevant triggering events for GBS. The concerns about the risk of inducing GBS in mass immunisation programmes against H1N1 2009 do not, therefore, seem justified by the available epidemiological data. However, the experiences from the 1976 swine flu vaccination programme emphasise the importance for active and passive surveillance to monitor vaccine safety.