title: Association between Guillain-Barré syndrome and influenza A (H1N1) 2009 monovalent inactivated vaccines in the USA: a meta-analysis.
abstract: BACKGROUND
  The influenza A (H1N1) 2009 monovalent vaccination programme was the largest mass vaccination initiative in recent US history. Commensurate with the size and scope of the vaccination programme, a project to monitor vaccine adverse events was undertaken, the most comprehensive safety surveillance agenda in the USA to date. The adverse event monitoring project identified an increased risk of Guillain-Barré syndrome after vaccination; however, some individual variability in results was noted. Guillain-Barré syndrome is a rare but serious health disorder in which a person's own immune system damages their nerve cells, causing muscle weakness, sometimes paralysis, and infrequently death. We did a meta-analysis of data from the adverse event monitoring project to ascertain whether influenza A (H1N1) 2009 monovalent inactivated vaccines used in the USA increased the risk of Guillain-Barré syndrome.
  
  
  METHODS
  Data were obtained from six adverse event monitoring systems. About 23 million vaccinated people were included in the analysis. The primary analysis entailed calculation of incidence rate ratios and attributable risks of excess cases of Guillain-Barré syndrome per million vaccinations. We used a self-controlled risk-interval design.
  
  
  RESULTS
  Influenza A (H1N1) 2009 monovalent inactivated vaccines were associated with a small increased risk of Guillain-Barré syndrome (incidence rate ratio 2·35, 95% CI 1·42-4·01, p=0·0003). This finding translated to about 1·6 excess cases of Guillain-Barré syndrome per million people vaccinated.
  
  
  CONCLUSIONS
  The modest risk of Guillain-Barré syndrome attributed to vaccination is consistent with previous estimates of the disorder after seasonal influenza vaccination. A risk of this small magnitude would be difficult to capture during routine seasonal influenza vaccine programmes, which have extensive, but comparatively less, safety monitoring. In view of the morbidity and mortality caused by 2009 H1N1 influenza and the effectiveness of the vaccine, clinicians, policy makers, and those eligible for vaccination should be assured that the benefits of inactivated pandemic vaccines greatly outweigh the risks.
  
  
  BACKGROUND
  US Federal Government.
authors.affiliation: National Vaccine Program Office, Office of the Assistant Secretary for Health, Department of Health and Human Services, Washington, DC, USA. dsalmon@jhsph.edu
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Salmon
authors.forename: Michael
authors.initials: M
authors.lastname: Proschan
authors.forename: Richard
authors.initials: R
authors.lastname: Forshee
authors.forename: Paul
authors.initials: P
authors.lastname: Gargiullo
authors.forename: William
authors.initials: W
authors.lastname: Bleser
authors.forename: Dale R
authors.initials: DR
authors.lastname: Burwen
authors.forename: Francesca
authors.initials: F
authors.lastname: Cunningham
authors.forename: Patrick
authors.initials: P
authors.lastname: Garman
authors.forename: Sharon K
authors.initials: SK
authors.lastname: Greene
authors.forename: Grace M
authors.initials: GM
authors.lastname: Lee
authors.forename: Claudia
authors.initials: C
authors.lastname: Vellozzi
authors.forename: W Katherine
authors.initials: WK
authors.lastname: Yih
authors.forename: Bruce
authors.initials: B
authors.lastname: Gellin
authors.forename: Nicole
authors.initials: N
authors.lastname: Lurie
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D020275:Guillain-Barre Syndrome / Q000139:chemically induced / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000009:adverse effects*; D007251:Influenza, Human / Q000517:prevention & control*; D008297:Male; D032541:Mass Vaccination / Q000009:adverse effects; D008875:Middle Aged; D058873:Pandemics / Q000517:prevention & control*; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D015164:Vaccines, Inactivated / Q000009:adverse effects; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines; D015164:Vaccines, Inactivated