Risk of Guillain-Barré Syndrome Among Older Adults Receiving Influenza Vaccine in Taiwan.

Importance: Although influenza vaccination has been associated with Guillain-Barré syndrome (GBS), the findings among studies of older adult populations are inconsistent. Objective: To determine the risk of GBS after influenza vaccination among older adults. Design, Setting, and Participants: This cross-sectional study incorporated a self-controlled case series design. Days 1 to 7, days 1 to 14, and days 1 to 42 after influenza vaccination were identified as risk intervals; days 8 to 180, days 15 to 180, and days 43 to 180 comprised the corresponding control interval. Population-based data were obtained from Taiwan's National Health Insurance research database between January 1, 2003, and December 31, 2017. Data were analyzed from November 1, 2021, through February 28, 2022. Adults 65 years or older who developed GBS within 180 days after influenza vaccination were enrolled. Exposure: Government-funded seasonal influenza vaccination. Main Outcomes and Measures: Onset of GBS during risk intervals after influenza vaccination compared with control intervals using Poisson regression to calculate incidence rate ratio (IRR). Results: Of 13 482 122 adults aged 65 years or older who received an influenza vaccination, 374 were hospitalized for GBS. The mean (SD) age of the study population was 75.0 (6.1) years; 215 (57.5%) were men and 159 (42.5%) were women. In terms of comorbidities, 33 adults (8.8%) had cancer and 4 (1.1%) had autoimmune diseases. The IRRs for GBS during days 1 to 7, days 1 to 14, and days 1 to 42 were 0.95 (95% CI, 0.55-1.61; P = .84), 0.87 (95% CI, 0.58-1.29; P = .48), and 0.92 (95% CI, 0.72-1.17; P = .49), respectively. No results showed statistical significance. Similarly, no significant differences in IRRs were noted for the overall risk interval (ie, days 1-42) in subgroup analyses pertaining to different age groups (65-74 years [0.93 (95% CI, 0.66-1.31)], 75-84 years [0.85 (95% CI, 0.58-1.26)], and ≥85 years [1.10 (95% CI, 0.57-2.11)]), sex (men, 0.97 [95% CI, 0.71-1.33; P = .87]; women, 0.85 [95% CI, 0.58-1.23; P = .39]), Charlson Comorbidity Index (1.03 [95% CI, 0.77-1.38; P = .84]), or comorbidities (cancer, 0.68 [95% CI, 0.28-1.64; P = .39]; autoimmune disease, 1.10 [95% CI, 0.11-10.53; P = .94]). Conclusions and Relevance: These findings suggest that influenza vaccination did not increase the risk of GBS among adults aged 65 years or older in Taiwan regardless of postvaccination period or underlying characteristics.