American Journal of Public Health
Volume 104, Issue 4 (April 2014)
http://ajph.aphapublications.org/toc/ajph/current

Cumulative Risk of Guillain–Barré Syndrome Among Vaccinated and Unvaccinated Populations During the 2009 H1N1 Influenza Pandemic
Claudia Vellozzi, MD, MPH, Shahed Iqbal, PhD, MBBS, MPH, Brock Stewart, PhD, Jerome Tokars, MD, MPH, and Frank DeStefano, MD, MPH
Claudia Vellozzi, Shahed Iqbal, Brock Stewart, and Frank DeStefano are with the Immunization Safety Office, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA. Jerome Tokars is with the Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention.
http://ajph.aphapublications.org/doi/abs/10.2105/AJPH.2013.301651

Abstract
Objectives. We sought to assess risk of Guillain–Barré syndrome (GBS) among influenza A (H1N1) 2009 monovalent (pH1N1) vaccinated and unvaccinated populations at the end of the 2009 pandemic.

Methods. We applied GBS surveillance data from a US population catchment area of 45 million from October 15, 2009, through May 31, 2010. GBS cases meeting Brighton Collaboration criteria were included. We calculated the incidence density ratio (IDR) among pH1N1 vaccinated and unvaccinated populations. We also estimated cumulative GBS risk using life table analysis. Additionally, we used vaccine coverage data and census population estimates to calculate denominators.

Results. There were 392 GBS cases; 64 (16%) occurred after pH1N1vaccination. The vaccinated population had lower average risk (IDR = 0.83, 95% confidence interval = 0.63, 1.08) and lower cumulative risk (6.6 vs 9.2 cases per million persons, P = .012) of GBS.

Conclusions. Our findings suggest that at the end of the influenza season cumulative GBS risk was less among the pH1N1vaccinated than the unvaccinated population, suggesting the benefit of vaccination as it relates to GBS. The observed potential protective effect on GBS attributed to vaccination warrants further study