(239) Background Incidence Rates of Guillain-Barre Syndrome in United States Older Adults at Risk of Respiratory Syncytial Virus in a Trial-Similar Real World Data Cohort

Background: Prevention of respiratory syncytial virus (RSV) lower respiratory tract infections in older adults was a significant unmet medical need before the recent introduction of safe and effective vaccines. Having accurate background incidence rates (BIR) of safety events is a crucial aspect of contextualizing findings during post-marketing pharmacovigilance. Data is sparse on the BIR of Guillain-Barre Syndrome (GBS) in older adults, a condition of interest due to a small number of reported cases in RSV vaccine clinical trials.

Objectives: To generate the BIR of GBS in a large, real-world population with similar characteristics to those in the RSV vaccine clinical trials.

Methods: In the US-based Optum, de-identified integrated electronic health records (EHR) database, a retrospective cohort was constructed among adults ≥ 60 years, restricting to integrated delivery networks. For the trial-similar cohorts, clinical trial inclusion and exclusion criteria (e.g., excluding those with history of anaphylaxis, chronic immunosuppressive therapies, serious chronic disorders, etc.) were applied to the EHR data using diagnostic and procedural codes. The source population cohorts consisted of all adults ≥ 60 years.
Analyses were stratified by pre-COVID-19 (2018-2019) and COVID-19 (2020-2021) eras to examine differences due to pandemic-related healthcare disruptions and a possible connection between COVID-19 infection and GBS. The BIR for GBS was calculated as the number of new events (identified using ICD-10 code G61.0 in the inpatient setting) within the follow-up period (all person-years [PY] available until censoring) divided by the total PY at risk. Any patients with prevalent events (those occurring in the washout period of 730 days prior to cohort entry) were excluded.

Results: In the pre-COVID-19 era, both the source population and trial-similar cohort included over 9 million people, while the COVID-19 era cohorts were slightly smaller (over 7 million). Participants were predominantly white non-Hispanic (56% female, 81% white, 1.5% Asian, 8% black, 3% Hispanic).
In the pre-COVID-19 era, the source population BIR was 4.5 per 100,000 PY (95% CI 4.2-4.8) and in the trial-similar cohort was 3.9 per 100,000 PY (95% CI 3.6-4.3). In the COVID-19 era, the source population BIR was 5.1 per 100,000 PY (95% CI 4.6-5.5) and trial-similar cohort was 4.6 per 100,000 PY (95% CI 4.1-5.1).

Conclusions: BIRs were similar to published rates in general population US older adults (4.6 per 100,000 PY in Moll et al. 2023). Rates were comparable across time periods, possibly due to the severe nature of GBS. Future analyses to validate findings in other US EHR data sources, as well as internationally, are needed.