Initial report was received via a search of the scientific literature on 23 August 2012. The following information is per the report: Active, population-based surveillance for GBS cases in persons who had an initial health-care encounter between October 1, 2009, and May 31, 2010, was conducted among 44.9 million residents at the 10 sites of the Emerging Infections Program (EIP). Each EIP site established a surveillance network comprised of neurologists and other health-care providers that was queried weekly to stimulate reporting of suspected GBS cases; hospital discharge data were also reviewed (International Classification of Disease, Ninth Revision) to capture additional cases not reported through the provider network. Trained surveillance officers reviewed medical records to gather standardized information on patient characteristics, clinical presentation, and medical history for every suspected GBS case. Suspected cases of GBS were evaluated by surveillance officers according to criteria established by the Brighton Collaboration. Patients with confirmed (Brighton levels 1 and 2) and probable (Brighton level 3) GBS were included in the analysis. Results: Among 44.9 million persons under surveillance from October 1, 2009, to May 31, 2010, study personnel identified 707 suspected GBS cases; 282 (40%) did not meet the Brighton criteria. Among the remaining 425 patients, a total of 411 GBS cases were included in the analysis (349 confirmed and 62 probable); 14 patients with GBS onset dates prior to October 1, 2009, were excluded. Eighty-five percent of GBS cases were aged >/= 25 years; 52% were male, 15% required mechanical ventilation, and 3% died. Of the 411 total cases of confirmed or probable GBS, 408 patients received pH1N1 vaccine [29 patients (27 confirmed and 2 probable) received pH1N1 vaccine during the 42 days prior to symptom onset; 379 patients received it outside of the 42 day timeframe] and 371 patients received seasonal vaccine [36 patients (30 confirmed and 6 probable) received pH1N1 vaccine during the 42 days prior to symptom onset; 335 patients received it outside of the 42 day timeframe]. Among the 29 patients who received pH1N1 vaccine during the 42 day timeframe, there were 17 cases where 1 or more antecedent events were documented. Also of the 29 cases, 11 patients experienced upper respiratory or influenza-like symptoms, 5 experienced mechanical ventilation, and 1 patient had a medical history of a prior episode of GBS. Among the 36 patients who received seasonal vaccine during the 42 day timeframe, there were 24 cases where 1 or more antecedent events were documented. Also of the 36 cases, 21 patients experienced upper respiratory or influenza-like symptoms and 4 experienced mechanical ventilation. (Specific antecedent events included: upper respiratory or influenza-like symptoms, fever, gastrointestinal symptoms, seasonal influenza vaccine, and noninfluenza vaccination.). There were a total of  11 cases of death. In the group of 408 patients who received pH1N1 vaccine, there was 1 fatal case within the 42 day timeframe and 10 fatal cases outside of the 42 day timeframe. In the group of 371 patients who received seasonal vaccine, there was 1 fatal case within the 42 day timeframe and 8 fatal cases outside of the 42 day timeframe. History of pH1N1 vaccination was ascertained for 408 GBS cases (99%), of whom 67 (16%) received pH1N1 vaccine. Of these 67 patients, pH1N1 vaccine was received during the 42 days prior to GBS onset for 29 (43%), more than 42 days prior to onset for 34 (51%), and after GBS onset for 4 (1%). Fifty-seven patients (85%) received inactivated vaccine, 4 (6%), the vaccine type was unknown. pH1N1 vaccination status was ascertained by means of vaccine administration records, state registries, or administering provider documentation for 79% of cases, with the remainder being ascertained by self-report. History of seasonal vaccination was ascertained for 90% (n=371) of GBS cases, of whom 131 (35%) received seasonal vaccine. Of these 131 patients, seasonal vaccine was received during the 42 days prior to GBS onset for 36 (27%), more than 42 days prior to onset for 90 (69%), and after GBS onset for 5 (4%). Sixty-nine patients (53%) received inactivated vaccine, 1 (1%) received live attenuated vaccine, and vaccine type was unknown for 61 (47%). Seasonal vaccination status was ascertained by means of documented sources for 63% of cases, with the remainder being ascertained by self-report. Five cases received both pH1N1 vaccine and seasonal vaccine during the 42 days prior to GBS onset. Among GBS cases receiving pH1N1 vaccine 1-84 days prior to GBS onset, the median interval between vaccine receipt and disease onset was 27 days. The most likely cluster identified using the scan statistic was 29 cases occurring during days 1-37, but this cluster was not statistically significant (P=0.13). For seasonal vaccine, the median interval was 36 days, and no statistically significant cluster was identified. Generally, demographic characteristics, medical history, and outcomes for GBS cases did not differ by vaccine status, although antecedent events were less common among cases who received pH1N1 vaccine during the 42 days prior to onset than among those who did not (59% vs. 79%; P = 0.02). Examination of specific types of antecedent events showed that upper respiratory or influenza like symptoms were the only category of antecedent event that was significantly less common among cases who received pH1N1 vaccine than among those who did not (38% vs. 67%; P < 0.01). The total number of observed GBS cases in the EIP catchment area (n = 411) was similar to the expected number for the surveillance population (age-adjusted observed/expected ratio = 1.21, 95% confidence interval (CI): 0.78, 1.81), as well as among persons aged <25 years and >=25 years. Authors estimated that there was less than 1 excess GBS case per million doses of pH1N1 vaccine administered and concluded that given the magnitude of morbidity and mortality associated with influenza infection, these findings provide reassurance that the excess risk of GBS following receipt of the pH1N1 vaccine was small compared with the morbidity and mortality prevented through the widespread use of the vaccine. 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