Guillain-Barré syndrome after H1N1 vaccination in the United States: a report using the CDC/FDA Vaccine Adverse Event Reporting System (2009).

BACKGROUND Although the Guillain-Barré syndrome (GBS) can be associated with the seasonal influenza vaccine, there is no definite evidence that GBS is associated with H1N1 influenza vaccination. The objective of this report is to study the occurrence and characteristics of GBS after H1N1 vaccine administration in the United States in 2009. METHODS Data were acquired from the Vaccine Adverse Event Reporting System and supplemented by additional information obtained from the Center for Biologics Evaluation and Research, under the Federal Freedom of Information Act. RESULTS A total of 62 individuals (mean age 46.51 ± 22.41 years), 33 of whom were men, developed GBS associated with the H1N1 influenza vaccination in 2009. Sixty GBS cases were reported within 6 weeks after vaccination, with 31 cases (50.0%) reported in the first 2 weeks. The estimated rate of occurrence of GBS was 6.2 cases per 10 million vaccinations, which is comparable to the rate of GBS in the general population. CONCLUSION The higher rate of GBS reports in the first 6 weeks after H1N1 vaccination suggests that some GBS cases may be triggered by H1N1 vaccination. This warrants early recognition, treatment, and active surveillance in the postvaccination setting.