Near real-time surveillance for Guillain-Barré syndrome after influenza vaccination among the Medicare population, 2010/11 to 2013/14.

BACKGROUND: Guillain-Barré syndrome (GBS) is a serious acute demyelinating disease that causes weakness and paralysis. The Food and Drug Administration (FDA) began collaborating with the Centers for Medicare and Medicaid Services (CMS) to develop near real-time vaccine safety surveillance capabilities in 2006 and has been monitoring for the risk of GBS after influenza vaccination for every influenza season since 2008.

METHODS: We present results from the 2010/11 to 2013/14 influenza seasons using the Updating Sequential Probability Ratio Test (USPRT), with an overall 1-sided α of 0.05 apportioned equally using a constant alpha-spending plan among 20 consecutive weekly tests, 5 ad hoc tests, and a 26th final end of season test. Observed signals were investigated using the self-controlled risk interval (SCRI) design.

RESULTS: Over 15 million people were vaccinated in each influenza season. In the 2010/11 influenza season, we observed an elevated GBS risk during the season, with an end of season SCRI analysis finding a nonsignificant increased risk (RR=1.25, 95% CI: 0.96-1.63). A sensitivity analysis applying the positive predictive value of the ICD-9 code for GBS from the 2009/10 season estimated a RR=1.98 (95% CI: 1.42-2.76). Although the 2010/11 influenza vaccine suggested an increased GBS risk, surveillance of the identical vaccine in the 2011/12 influenza season did not find an increased GBS risk after vaccination. No signal was observed in the subsequent three influenza seasons.

CONCLUSIONS: Conducting near real-time surveillance using USPRT has proven to be an excellent method for near real-time GBS surveillance after influenza vaccination, as demonstrated by our surveillance efforts during the 2010/11-2013/14 influenza seasons. In the 2010/2011 influenza season, in addition to the 2009 H1N1 influenza pandemic, using near real-time surveillance we were able to observe a signal early in the influenza season and the method has now become routine.