(332) Background Rates of Neuroinflammatory Disorders and Atrial Fibrillation – Conditions of Interest for Vaccine Safety Studies

Background: Guillain-Barré Syndrome (GBS), acute disseminated encephalomyelitis (ADEM), and atrial fibrillation/flutter (AF) are conditions of interest to vaccine safety including respiratory syncytial virus (RSV) vaccines.

Objectives: To estimate rates and assess infection status and seasonality of new-onset ADEM, GBS, and AF, and recurrent AF, among older adults in the US.

Methods: Using US claims data (MerativeTM MarketScan® Commercial and Medicare Databases) from Jan 2017 through Dec 2022 we identified individuals ≥60 yrs old with medical and drug coverage in the 365 days prior to first ICD-10-CM diagnosis code of interest; a coverage gap of ≤ 45 days was allowed. New-onset GBS and ADEM were defined by either (a) ≥1 inpatient principal discharge diagnosis or, (b) ≥1 inpatient diagnosis (any position) and a preceding ambulatory diagnosis (outpatient or emergency department) within 7 days prior to hospital admission. New-onset AF was defined by (a) ≥1 inpatient diagnosis in any position or, (b) ≥2 ambulatory diagnoses ≥7 days apart and within 90 days of one another. A 365-day washout was applied to all new-onset conditions. Recurrent AF required (a) ≥1 inpatient diagnosis in any position and (b) history of ≥1 inpatient or ≥2 ambulatory diagnoses within 365 days of admission. We assessed infection status and seasonality and calculated rates per 10K eligible member-years (MY) and 95% confidence intervals (95% CI) for each condition overall and stratified by age, sex, and month/year.

Results: We identified 437 GBS cases with a rate of 0.33 per 10K MY (95% CI 0.30 – 0.36). There were 14 ADEM cases with a rate of 0.01 per 10K MY (95% CI 0.01 – 0.02). Rates of new-onset AF (n=199,540) and recurrent AF (n=153,725) were 160.8 per 10K MY (95% CI 160.1 - 161.5) and 2,661 per 10K MY (95% CI 2,647 – 2,674), respectively. Evidence of an infection (respiratory, gastrointestinal, or unspecified viral) on the event date was similar among those with GBS and ADEM (20%) and most were respiratory infections (78% and 100%, respectively). GBS and new-onset AF rates were higher in males vs females (GBS: 0.41 vs 0.26 per 10K MY; AF: 200.9 vs 127.4 per 10K MY); recurrent AF was higher in females (2,847 vs 2,529 per 10K MY). Increasing rates with older age were observed for new-onset and recurrent AF cohorts while GBS rates peaked among 70–74-year-old persons. We observed decreases in the rates of new and recurrent AF during the first year of the COVID-19 pandemic. Pre-pandemic, AF rates were highest in January through May (2017 – 2019).

Conclusions: We have estimated rates of ADEM, GBS, and AF among older adults and observed trends that can inform feasibility and sample size assessments for future evaluations of post-marketing vaccine safety for RSV and other vaccines.