New scientific confirmation of the low risk of Guillain-Barréovog syndrome associated with the use of pandemic flu vaccine in the vaccination season 2009/2010
According to the results of an extensive meta-analysis conducted in the USA and recently published in The Lancet magazine, monovalent inactivated vaccines against pandemic influenza AH1N1 are associated with a minor risk of Guillain-Barréovog syndrome (GBS)1.
The aim of the research was to ascertain how great a risk can be associated with the use of the aforementioned vaccines in relation to the expected number of GBS cases. GBS is a rare autoimmune disorder in which a person’s own immune system damages their nerve cells, causing muscle weakness and paralysis. It is very often associated with colds and other infections of the upper respiratory system, the flu (seasonal or any other) and syndromes similar to the flu and some infections of the digestive system.
A comprehensive analysis of the safety risks associated with the use of the vaccines, funded by the American government, analysed data obtained from six adverse event monitoring systems that included information on 23 million vaccinated people in the USA. The incidence rate ratio (IRR) for the development of GBS was 2.35 (95% CI 1.42 -4.01, p = 0.0003). With the assumption that the background rate of GBS is one case per 100,000 people a year, the incidence rate ratio means translates to about 1.6 excess cases of GBS per million people vaccinated.
The small risk confirms the previous estimates of GBS after seasonal influenza vaccination. Furthermore, this risk was consistent in different adverse event monitoring systems, with a more extensive definition of GBS, across different age groups and independently of concurrent seasonal influenza vaccination.
In light of the morbidity and mortality caused by 2009/2010 H1N1 influenza, the authors of the meta-analysis conclude that given the effectiveness of the vaccine, the use of inactivated pandemic vaccines greatly outweigh the risks and that doctors, politicians and those eligible for vaccination against influenza should be aware of that.
1 Salmon D.A. et al. Association between Guillain-Barré syndrome and influenza A (H1N1) 2009 monovalent inactivated vaccines in the USA: a meta-analysis. The Lancet, 13 April 2013, available at: http://dx.doi.org/10.1016/S0140-6736(12)62189-8