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Pandemic vaccines and small excess of Guillain-Barré cases

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f1714 (Published 20 March 2013) Cite this as: BMJ 2013;346:f1714

US researchers have identified a small excess risk of Guillain-Barré syndrome associated with vaccination against pandemic influenza (H1N1). National surveillance systems captured 77 cases of the syndrome in 23 million vaccinated people. Twice as many diagnoses occurred in the 42 days after vaccination as in a control period—50-91 days after vaccination (54 v 23; incidence rate ratio 2.35, 90% CI 1.53 to 3.68). The authors estimate that pandemic vaccines were associated with an extra 1.6 cases of the syndrome per million people vaccinated.

They combined data from six surveillance systems operating in the US during the 2009 pandemic. The same signal emerged from a series of different analyses, and the authors are confident that it’s real and not a statistical quirk. US vaccination programmes used inactivated monovalent vaccines against H1N1. Vaccination prevented an estimated 700 000 to 1.5 million cases of influenza, and saved 200-500 lives nationwide.

A causal association between inactivated pandemic vaccines and Guillain-Barré syndrome is plausible but impossible to prove, because the syndrome is also associated with flu and with the flu season, say the authors. Absolute risks linked to vaccines remain very low, however, much lower than the risks associated with influenza H1N1. More than 60 million cases of flu were reported to US authorities during the pandemic, and 12 470 people died.

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Cite this as: BMJ 2013;346:f1714