P-711. Persistence of Immunogenicity and Safety of the Respiratory Syncytial Virus Prefusion F Protein Vaccine (RSVPreF3 OA) Administered to Adults 50–59 Years of Age (YOA)

Abstract Background The immune response induced by RSVPreF3 OA in adults 50–59 YOA, including adults with chronic conditions that increase the risk for RSV disease, was non-inferior in terms of RSV-A/-B neutralization titers compared to that in older adults (≥ 60 YOA) at 1 month (M) post-vaccination. Methods This was a phase 3, observer-blind, placebo-controlled multi-country study (NCT05590403). Adults 50–59 YOA at increased risk (AIR) for RSV disease due to specific chronic conditions and not at increased risk for RSV disease (non-AIR) 50–59 YOA adults were randomized (2:1) to receive 1 dose of RSVPreF3 OA (AIR-RSV, non-AIR-RSV) or placebo (AIR-placebo, non-AIR-placebo). A control group of adults ≥ 60 YOA received RSVPreF3 OA (RSV-OA). We assessed the immune response at 1M and 6M post-vaccination. Humoral immunity (HI) and cell-mediated immunity (CMI) were assessed in terms of RSV-A/-B neutralization titers and RSVPreF3-specific CD4+ T-cell frequencies. Safety up to study end (12M post-vaccination) was also assessed. Results 1533 participants received RSVPreF3 OA or placebo. In all RSV groups, RSV-A/-B neutralization titers (Figure 1) and RSVPreF3-specific CD4+ T-cell frequencies (Figure 2) increased substantially from pre-vaccination to 1M post-vaccination and remained above baseline levels at 6M (4.9–5.2-fold for RSV-A and 3.3–3.6-fold RSV-B neutralization titers). Within 6M post-vaccination, 3.9% (AIR-RSV), 0.8% (non-AIR-RSV), 2.1% (AIR-placebo, non-AIR-placebo) and 2.4% (RSV-OA) of participants reported serious adverse events (SAEs). Eight potential immune-mediated diseases (AIR-RSV: 4; AIR-placebo: 1; RSV-OA: 3) were reported within 6M post-vaccination. Of these, one case of cold type hemolytic anemia (RSV-OA, onset at day 53 post-vaccination, also SAE) was considered vaccine-related by the investigator. Five deaths (AIR-RSV: 4; AIR-placebo: 1), none considered vaccine-related, were reported up to study end (12M). Conclusion At 6M post-vaccination, HI and CMI remained above baseline both in RSVPreF3 OA-vaccinated adults 50–59 YOA with/without chronic conditions and in adults ≥60 YOA (RSV-OA). Up to 12M, the safety profile in adults 50–59 YOA was similar to the safety profile in those ≥ 60 YOA and was considered acceptable. Funding: GSK Disclosures Murdo Ferguson, MD, GSK: Study related payments for training and the conduct of the study as a study site Tino F. Schwarz, Prof. Dr. MD, AstraZeneca: Honoraria|Bavarian Nordic: Advisor/Consultant|Bavarian Nordic: Honoraria|Biogen: Honoraria|Biontech: Advisor/Consultant|Biontech: Honoraria|CSL Vifor: Honoraria|CSL-Seqirus: Advisor/Consultant|CSL-Seqirus: Honoraria|Diasorin: Honoraria|GSK: Advisor/Consultant|GSK: Honoraria|Janssen-Cilag: Honoraria|Merck-Serono: Honoraria|Moderna: Advisor/Consultant|Moderna: Honoraria|MSD: Honoraria|Novavax: Advisor/Consultant|Novavax: Honoraria|Pfiser: Honoraria|Roche: Honoraria|Sanofi-Aventis: Honoraria|Synlab: Honoraria|Takeda: Advisor/Consultant|Takeda: Honoraria Sebastián A. Núñez, Dr., GSK: Support for attending meetings and/or travel Juan Rodríguez García, MD, GSK: Advisor/Consultant|GSK: Grant/Research Support|GSK: Honoraria|Pfizer: Honoraria|Pfizer: Support for attending meetings and/or travel|Sanofi: Honoraria|Sanofi: Support for attending meetings and/or travel Carlos Zala, MD, GSK: Grant/Research Support|GSK: Support for attending meetings and/or travel (EACS 2023) Josef Grosskopf, MD, GSK: Advisor/Consultant|GSK: Expert Testimony|GSK: Grant/Research Support|GSK: Honoraria|GSK: Support for attending meetings and/or travel|Lilly: Grant/Research Support|New Amsterdam Pharma: Grant/Research Support|Novartis: Grant/Research Support|Pharmalog: Grant/Research Support|Syneos: Grant/Research Support|Winecker Pharma: Grant/Research Support Christine Voors-Pette, MD, QPS Netherlands B.V.: Ex-Employee of QPS Netherlands B.V. Hiwot Amare Hailemariam, MD, PhD, GSK: Salary as GSK employee with stock options|GSK: Stocks/Bonds (Public Company) Caroline Portaels, DVM, GSK: Salary as GSK employee with stock options|GSK: Stocks/Bonds (Public Company) Magali de Heusch, PhD, GSK: Salary as GSK employee with stock options|GSK: Stocks/Bonds (Public Company) Bruno Salaun, PhD, GSK: Salary as GSK employee with stock options|GSK: Stocks/Bonds (Public Company) Silvia Damaso, MSc, GSK: Salary as GSK employee with stock options|GSK: Stocks/Bonds (Public Company) Marie-Pierre David, Master in Statistics, GSK: As GSK employee, I’m part of a patent application|GSK: Salary as GSK employee with stock options|GSK: Stocks/Bonds (Public Company) Dominique Descamps, MD, GSK: Salary as GSK employee with stock options|GSK: Stocks/Bonds (Public Company) Judith Hill, Dr., GSK: Salary as GSK employee with stock options|GSK: Stocks/Bonds (Public Company) Corinne Vandermeulen, MD, PhD, GSK: Salary as GSK employee with stock options|GSK: Stocks/Bonds (Public Company) Veronica Hulstrøm, MD, PhD, GSK: Salary as GSK employee with stock options|GSK: Stocks/Bonds (Public Company)