Background: The U.S. Food and Drug Administration and the Centers for Medicare & Medicaid Services have been actively monitoring the risk of Guillain-Barré syndrome (GBS) following influenza vaccination among Fee-for-Service (FFS) Medicare beneficiaries every season since 2008. We present our evaluation of the GBS risk following influenza vaccinations during the 2017-2018 season.

Methods: We implemented a multilayered approach to active safety surveillance that included near real-time surveillance early in the season, comparing GBS rates post-vaccination during the 2017-2018 season with rates from five prior seasons using the Updating Sequential Probability Ratio Test (USPRT), and end-of-season self-controlled risk interval (SCRI) analyses.

Results: We identified approximately 16 million influenza vaccinations. The near real-time surveillance did not signal for a potential 2.5-fold increased GBS risk either in days 8-21 or 1-42 post-influenza vaccination. In the SCRI analyses, we did not detect statistically significant increased GBS risks among influenza-vaccinated Medicare beneficiaries ≥65 years for either the 8-21 or 1-42-day risk windows for all seasonal vaccines combined, high-dose vaccine, or standard-dose vaccines; we did detect an increased GBS risk in days 8-21 post-vaccination for individuals vaccinated with the adjuvanted vaccine (OR: 3.75; 95% CI: 1.01, 13.96), although this finding was not statistically significant after multiplicity adjustment (p = 0.146).

Conclusions: Our multilayered surveillance approach-which allows for early detection of elevated GBS risk and provides reliable end-of-season SCRI estimates of effect size-did not identify an increased GBS risk following 2017-2018 influenza vaccinations. The slightly increased GBS risk with the adjuvanted vaccine, which was not statistically significant following multiplicity adjustment, is consistent with the package inserts of all U.S.-licensed influenza vaccines, which warn of a potential low increased GBS risk. The benefits of influenza vaccines in preventing morbidity and mortality heavily outweigh this potential risk.