Importance: The United States Food and Drug Administration conducts routine post-market surveillance of approved vaccines to identify and characterize health outcomes risk associated with vaccination. Pre-licensure clinical trials of RSVPreF3+AS01 and RSVPreF vaccines identified a small number of Guillain-Barré syndrome cases, a serious acute demyelinating disease, following vaccination. Objective: To use Centers for Medicare & Medicaid Services Medicare Fee-for-Service administrative claims and Medicare Part D data to evaluate risk of Guillain-Barré syndrome following respiratory syncytial virus vaccination. Design, Settings, and Participants: We studied vaccines administered between May 3, 2023, when vaccines were first approved, through January 28, 2024. This self-controlled case series study design compared the incidence of Guillain-Barré syndrome during risk intervals of 1–42 days following vaccination to the incidence in subsequent control intervals (43–90 days) among Medicare beneficiaries, aged 65 years and older, enrolled in Fee-for-Service and Medicare Part D. Exposures: Receipt of a single dose of RSVPreF3+AS01 or RSVPreF vaccines. Outcomes: Guillain-Barré syndrome was identified using diagnosis code G61.0 in the primary diagnosis position on hospital inpatient claims; returned cases were confirmed via medical record review using Brighton Collaboration’s case definition. Results: We captured approximately 3.23 million Medicare beneficiaries that received respiratory syncytial virus vaccination during the study period. A total of 95 incident Guillain-Barré syndrome cases were observed following respiratory syncytial virus vaccination. In our chart-confirmed self-controlled case series analysis, we observed an increased incidence of Guillain-Barré syndrome following RSVPreF3+AS01 (IRR: 2.46, [95% CI: 1.19, 5.08]) with an attributable risk of 6.5 cases per 1 million doses. We observed an increased, yet not statistically significant, incidence of Guillain-Barré syndrome following RSVPreF (IRR: 2.02, [95% CI: 0.93, 4.40]) with an attributable risk of 9 cases per 1 million doses. Conclusion and Relevance: Findings from this self-controlled case series study suggest an increased risk of Guillain-Barré syndrome during 1-42 days following respiratory syncytial virus vaccination, with fewer than 10 excess Guillain-Barré syndrome cases per 1 million vaccine doses among Medicare beneficiaries 65 years and older. The U.S. Food and Drug Administration maintains that the substantial benefits of RSV vaccination outweigh these identified risks associated with vaccines. Key Points: Question: Is there an increased risk of developing Guillain-Barré syndrome (GBS) following vaccination with RSVPreF3+AS01 (AREXVY®) and RSVPreF (ABRYSVO®) among Medicare beneficiaries aged 65 years and older? Findings: In a self-controlled case series analysis of Medicare beneficiaries with medical record review, we estimated the incidence rate ratio (IRR) comparing GBS in pre-specified risk and control intervals following vaccination with RSVPreF3+AS01 (IRR: 2.46, 95%CI: 1.19-5.08) or RSVPreF (IRR: 2.02, 95%CI: 0.93-4.40). RSV vaccines were associated with fewer than 10 excess GBS cases per 1 million vaccine doses. Meaning: These findings suggest an increased risk of GBS following RSV vaccination.

COVID-19 infections have contributed to substantial increases in hospitalizations. This study describes demographics, baseline clinical characteristics and treatments, and clinical outcomes among U.S. patients admitted to hospitals with COVID-19 during the prevaccine phase of the pandemic. A total of 20,446 hospitalized patients with a positive COVID-19 nucleic acid amplification test were identified from three large electronic health record databases during 5 February–30 November 2020 (Academic Health System: n = 4504; Explorys; n = 7492; OneFlorida: n = 8450). Over 90% of patients were ≥30 years of age, with an even distribution between sexes. At least one comorbidity was recorded in 84.6–96.1% of patients; cardiovascular and respiratory conditions (28.8–50.3%) and diabetes (25.6–44.4%) were most common. Anticoagulants were the most frequently reported medications on or up to 28 days after admission (44.5–81.7%). Remdesivir was administered to 14.1–24.6% of patients and increased over time. Patients exhibited higher COVID-19 severity 14 days following admission than the 14 days prior to and on admission. The length of in-patient hospital stay ranged from a median of 4 to 6 days, and over 85% of patients were discharged alive. These results promote understanding of the clinical characteristics and hospital-resource utilization associated with hospitalized COVID-19 over time.