P-97. Safety, Tolerability, and Immunogenicity of Revaccination With mRNA-1345, an Investigational Vaccine Against RSV, Given at 12 Months Following a Primary Dose in Adults Aged ≥ 50 Years

Abstract Background mRNA-1345 is an investigational RSV vaccine that has demonstrated efficacy for the prevention of lower-respiratory tract disease in older adults. The duration of protection and need for revaccination have not yet been defined. Interim findings are presented from a phase 3 trial evaluating mRNA-1345 revaccination at 12 months after a primary dose in adults aged ≥ 50 years. Figure 1. Methods Part C of a multi-part, ongoing, phase 3 trial (NCT05330975) evaluated the safety, tolerability, and immunogenicity of open-label revaccination with mRNA-1345 (50 µg) in participants aged ≥ 50 years who previously received a primary dose of mRNA-1345 in Part B of the trial. Safety, tolerability, and immunogenicity (RSV-A and RSV-B neutralizing antibody [nAb] responses) of revaccination were primary objectives. Non-inferiority of immune responses was assessed via geometric mean titer ratio (GMR; 95% CI lower bound > 0.667) at Day 29 post-revaccination (Part C) versus Day 29 post-primary dose (Part B). Results of the Day 29 post-revaccination interim analysis are presented here. Results Overall, 543 participants were revaccinated with mRNA-1345 (50 µg). Solicited local and systemic adverse reactions within 7 days post revaccination were reported by 55.8% and 50.3% of participants, respectively. Injection site pain (54.3%), headache (33.5%), myalgia (33.5%), fatigue (31.1%), and arthralgia (28.5%) were most frequently reported (≥ 20%) and were primarily grade 1 or 2 in severity. Up to 28 days after revaccination, no adverse events (AEs) led to study discontinuation, and no fatalities or vaccine-related serious AEs, AEs of special interest, or severe AEs were reported. All coprimary immunogenicity endpoints met pre-specified criteria for non-inferiority based on Day 29 GMRs (revaccination Day 29 vs primary Day 29); nAb GMRs (95% CI) were 1.08 (0.99, 1.17) for RSV-A and 0.91 (0.84, 0.99) for RSV-B (Figure 1). Conclusion Revaccination with mRNA-1345 administered 12 months after a primary dose was well-tolerated, had no identified safety concerns, and elicited RSV nAbs at Day 29 that were non-inferior to those after a primary mRNA-1345 dose in adults aged ≥ 50 years. These data support mRNA-1345 revaccination at 12 months after primary vaccination if the need for revaccination is determined. Disclosures Jaya Goswami, MD, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Denise C. Hsu, MD, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Alana Simorellis, PhD, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Lauren Wilson, MSN, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Rakesh Dhar, MD, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Xiaowei Wang, PhD, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Archana Kapoor, PhD, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Avi Collins, BScN, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Vinicius Righi, PharmD, MBA, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Lan Lan, PhD, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Jiejun Du, PhD, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Honghong Zhou, Ph.D., Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Sonia K. Stoszek, PhD, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Christine A. Shaw, PhD, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Caroline Reuter, MD, MSCI, Moderna, inc.: Employee|Moderna, inc.: Stocks/Bonds (Public Company) Eleanor Wilson, MD, MHS, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Jacqueline Miller, MD, Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company) Rituparna Das, M.D., Moderna, Inc.: Employee|Moderna, Inc.: Stocks/Bonds (Public Company)