[Source: World Health Organization, full PDF document: (LINK). Extract, edited.]
Weekly epidemiological record / Relevé épidémiologique hebdomadaire
8 FéVRIER 2013, 88th year / 8 FéVRIER 2013, 88e année - No. 6, 2013, 88, 65–72 - http://www.who.int/wer
Global Advisory Committee on Vaccine Safety, December 2012
Pandemic influenza vaccines
GACVS reviewed 2 safety updates on influenza A(H1N1) pdm09 vaccines, which included associations with narcolepsy and with GBS. The association between use of the adjuvanted pandemic vaccine Pandemrix® (Glaxo-SmithKline) and abrupt juvenile narcolepsy has thus far been confirmed in 4 countries (Finland, Ireland, Norway and Sweden) with high uptake of vaccine among children and adolescents.
In all these countries the absolute risk was low but the relative risk was significantly raised, ranging from 6.6 (95% confidence interval [CI]: 3.1–14.5) in Sweden to 13.0 per 100 000 (95% CI: 4.8–34.7) in Ireland. An association in adults has so far been observed only in France.
Additional studies are also being finalized in the United Kingdom (UK) and Canada.
Although this vaccine is no longer being used and all lots of Pandemrix® (2009 H1N1) have now expired, GACVS considered that research should continue to better characterize the possible underlying biological mechanisms of this association. Most cases of narcolepsy, with or without exposure to Pandemrix®, occur in subjects who carry the HLA DQB1*0602 allele. The importance of understanding the triggers and causes of this association will be crucial, especially since new vaccines will be required to protect against future pandemics.
The association between GBS and influenza vaccine first emerged following swine influenza vaccination in the USA in 1976 (attributable risk: around 1 case of GBS per 100 000 vaccinations). GBS is a relatively rare (1–2 cases per 100 000 persons annually) acute peripheral immune-mediated neuropathy. In up to two-thirds of cases, GBS is preceded by an infectious illness, particularly a gastrointestinal or respiratory infection. The most frequently identified pathogen associated with subsequent GBS is Campylobacter jejuni (estimated at 1 GBS case per 3000 infectious episodes).
After 1976, several studies demonstrated no increased or a slightly increased risk of GBS after use of human seasonal influenza vaccines but vigilance remains high and GBS was carefully monitored during the influenza A(H1N1)pdm09 pandemic vaccination campaign.
GACVS has reviewed published and unpublished active surveillance studies that monitored GBS cases during influenza A(H1N1)pdm09 pandemic vaccination. The data are from single countries such as Canada, France, Germany, Sweden, the UK and the USA as well as a multinational European Union study and a global study.
Some but not all of these studies have shown a relative incidence of GBS of 2.28 to 3.76 following both unadjuvanted and adjuvanted influenza A(H1N1)pdm09 pandemic vaccines. Overall, the data available are compatible with a small increased risk of GBS after influenza A(H1N1)pdm09 vaccination that is substantially lower than that observed following the 1976 swine influenza vaccination campaign in the USA.