Late Breaking Abstract - Immunogenicity and safety of AS01E-adjuvanted respiratory syncytial virus prefusion F protein vaccine (adjuvanted RSVPreF3) up to 6 months post-vaccination in adults 18–49 years of age (YOA) at increased risk of RSV disease and adults ≥60 YOA

<bold>Background:</bold> Adults 18–49 YOA with certain chronic conditions are at increased risk for RSV disease (AIR). Immunogenicity of adjuvanted RSVPreF3 was non-inferior in 18–49 YOA AIR versus adults ≥60 YOA at 1 month (M) post-vaccination. <bold>Methods:</bold> In this open-label, multi-country study (<ext-link>NCT06389487</ext-link>), 18–49 YOA AIR and adults ≥60 YOA received 1 dose of adjuvanted RSVPreF3. Immunogenicity (RSV-A/-B neutralising titres) and safety were assessed up to 6M post-vaccination. <bold>Results:</bold> 1458 adults were vaccinated. RSV-A/-B neutralising titres increased from baseline to 1M post-vaccination and declined but remained well above baseline at 6M (Fig 1). While intensity and duration were similar across groups, frequency of reactogenicity was higher in 18–49 YOA AIR. Safety was overall consistent (Fig 2). <bold>Conclusion:</bold> Up to 6M post-vaccination, adjuvanted RSVPreF3 had a similar immunogenicity and overall consistent safety profile in 18–49 YOA AIR and ≥60 YOA adults, in whom efficacy was previously demonstrated. <bold>Funding:</bold> GSK <fig><object-id>erj;66/suppl_69/OA5521/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig> <fig><object-id>erj;66/suppl_69/OA5521/F2</object-id><object-id>F2</object-id><object-id>F2</object-id><graphic></graphic></fig>