Pandemic influenza A vaccination and incidence of Guillain-Barré syndrome in Korea.

Background: Many studies have investigated the association between Guillain-Barré syndrome (GBS) and vaccinations during the influenza A H1N1 pandemic of 2009 (pH1N1). Based on a nationally representative sample, we estimated the incidence of GBS during the pandemic period in Korea.

Materials And Methods: All medical records of GBS cases were reviewed in 28 randomly selected hospitals during 2008-2010, and the number of GBS cases at the national level was extrapolated using emergency care utilization data. The GBS rate per 100,000 person-years was estimated in the reference and pandemic periods.

Results: The incidence of GBS was 0.63 (95% CI: 0.37-0.89) per 100,000 person-years in the reference period and 0.87 (0.49-1.26) in the pandemic period. During the vaccination season, the pandemic period GBS incidence rate was not significantly higher than the reference period incidence rate (rate ratio: 1.52; 0.99-2.32), but difference was observed among persons aged 20-34 years. Rate of GBS increased after pH1N1 vaccination compared to the reference period (1.46, 1.26-1.68).

Discussion: The incidence of GBS increased slightly but not significantly during the pandemic period, although pH1N1 vaccination increased the GBS rate. Therefore, mass influenza vaccination programs should not be precluded on the basis of GBS.