P-45. A Phase 3, Randomized Trial Investigating the Safety, Tolerability, and Immunogenicity of V116, an Investigational Adult-Specific Pneumococcal Conjugate Vaccine, in Pneumococcal Vaccine-Naïve Adults 18–64 Years of Age with Increased Risk for Pn

Abstract Background Adults with certain underlying chronic medical conditions are at increased risk of pneumococcal disease (PD). V116 is an investigational, 21-valent, adult-specific pneumococcal conjugate vaccine (PCV) containing the most prevalent serotypes (STs) associated with PD in adults from regions with established pediatric vaccination programs. The Phase 3 STRIDE-8 study (NCT05696080) evaluated the safety and tolerability of V116 in adults 18–64 years of age at increased risk of PD. Immunogenicity of V116 was compared with sequential administration of 15-valent PCV (PCV15) followed by 23-valent pneumococcal polysaccharide vaccine (PPSV23). Methods Pneumococcal vaccine-naïve participants with ≥1 underlying chronic medical conditions (including diabetes mellitus, heart disease, kidney disease, liver disease, and lung disease) at increased risk of PD were randomized 3:1 to receive one dose of V116 on Day 1 followed by placebo at Week 8 or one dose of PCV15 on Day 1 followed by one dose of PPSV23 at Week 8. Safety was evaluated as the proportion of participants with adverse events (AEs). Immunogenicity was assessed by serotype-specific opsonophagocytic activity (OPA) geometric mean titers (GMTs) and immunoglobulin G (IgG) geometric mean concentrations (GMCs) for STs in V116 at baseline (Day 1) and 30 days post-vaccination (Day 30 for V116 + placebo and Week 12 for PCV15 + PPSV23). Results Of 518 participants randomized, 516 were vaccinated and received either V116 (n=386) or PCV15 (n=130) on Day 1; 96.7% of participants completed the trial. One or more AEs occurred in 265 (68.7%) and 118 (90.8%) participants vaccinated with V116 + placebo or PCV15 + PPSV23, respectively (Table 1). V116 was immunogenic for all 21 STs based on OPA GMTs, with comparable responses to PCV15 + PPSV23 for the 13 STs common to V116 and PCV15 + PPSV23, and higher responses for the eight STs unique to V116 (Figure 1). IgG GMCs were consistent with OPA GMTs (Figure 2). Conclusion V116 is well tolerated and immunogenic in adults 18–64 years of age at increased risk of PD, with comparable immune responses to PCV15 + PPSV23 for common STs and higher immune responses for unique STs. These findings support V116 as a novel population-specific vaccine for the prevention of PD in adults with chronic medical conditions at increased risk of PD. Disclosures Paul Scott, MD, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Jayani Pathirana, MBBS, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Michael Nissen, MD, CSL Seqirus: Education|GSK: Education|Pfizer: Education Amy Falk Russell, MS, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Doreen Fernsler, BS, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Muhammad Waleed, PhD, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Jianing Li, PhD, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Ulrike K. Buchwald, MD, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company) Heather L. Platt, MD, Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Employee|Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA: Stocks/Bonds (Private Company)