Guillain–Barré Syndrome Following Recombinant Zoster Vaccine in US Medicare Adults Age 65 Years or Older

BACKGROUND AND OBJECTIVE: Pre- and post-marketing studies detected Guillain-Barré syndrome following recombinant zoster vaccine. This study evaluated new-onset Guillain-Barré syndrome following recombinant zoster vaccine in older US adults. METHODS: Using the Medicare Chronic Condition Warehouse administrative data, we implemented a self-controlled risk interval case-only design with a 1- to 42-day risk window and a 43- to 84-day control window following recombinant zoster vaccine. Participants were Medicare beneficiaries aged ≥65 years who received at least one dose of the recombinant zoster vaccine two-dose regimen from 2018 to 2020. New-onset Guillain-Barré syndrome was identified using an algorithm requiring an International Classification of Disease, Tenth Revision diagnosis code of G61.0 in the primary position in an inpatient setting or in any other setting followed by an inpatient encounter within 7 days, with no Guillain-Barré syndrome in the preceding 365 days. Conditional Poisson regression models estimated the relative risk and 95% confidence intervals (CIs). We estimated the attributable risk and 95% CI. Sensitivity analyses examined dose-specific effects, 60- to 183-day dose spacing, and coronavirus disease 2019 and seasonality. RESULTS: Of 3,383,799 eligible participants, 75 experienced new-onset Guillain-Barré syndrome. The primary analysis detected a relative risk of 3.15 (95% CI 1.82, 5.68) and an attributable risk of 6.59 per 1,000,000 doses (95% CI 4.35, 7.96). The dose-specific analysis detected a relative risk of 5.33 (95% CI 2.59, 12.36) for dose 1. The coronavirus disease 2019 and seasonality analyses revealed an increased risk. Dose 2 and the 60- to 183-day dose spacing were not significant. CONCLUSIONS: The elevated risk of new-onset Guillain-Barré syndrome among US Medicare beneficiaries aged ≥65 years was detected after recombinant zoster vaccine dose 1 but not dose 2.