Cumulative risk of Guillain-Barré syndrome among vaccinated and unvaccinated populations during the 2009 H1N1 influenza pandemic

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.

FIGURE 1—

Cumulative risk of Guillain–Barré among the pH1N1 vaccinated and unvaccinated groups by date and all ages combined: Emerging Infections Program catchment area, October 15, 2009—May 31, 2010. Note. pH1N1 = influenza A (H1N1) 2009. The Emerging Infections Program includes 10 sites: California (3 counties), Colorado (5 counties), Connecticut, Georgia (8 counties), Maryland, Minnesota, New Mexico, New York (excluding New York City), Oregon (3 counties), and Tennessee.

FIGURE 2—

Proportion of ILI and laboratory confirmed influenza by virus strain type, and pH1N1 vaccinations by week: Emerging Infections Program catchment area, October 2009—May 2010. Note. ILI = influenza-like illness; pH1N1 = influenza A (H1N1) 2009. The Emerging Infections Program includes 10 sites: California (3 counties), Colorado (5 counties), Connecticut, Georgia (8 counties), Maryland, Minnesota, New Mexico, New York (excluding New York City), Oregon (3 counties), and Tennessee. ^aLaboratory confirmed cases from laboratories participating in the Centers for Disease Control and Prevention Viral Surveillance System (US and World Health Organization Collaborating Laboratories and National Respiratory and Enteric Virus Surveillance System). ^bThe weekly percentage of outpatient visits for ILI among ILINet sentinel physicians in the Emerging Infections Program catchment area.