Long-term Immunogenicity and Safety Profile of the Adjuvanted RSVPreF3 Vaccine in Korean Older Adults: A Sub-analysis of a Phase 3 Trial

BACKGROUND: Respiratory syncytial virus (RSV) poses substantial health risks to elderly adults and adults with certain underlying conditions. In a multi-country phase 3 trial (AReSVi-006), the adjuvanted RSVPreF3 vaccine has shown high efficacy against RSV disease. This post-hoc sub-analysis assessed immunogenicity, immunopersistence up to 24 months, and safety of a single dose of the adjuvanted RSVPreF3 vaccine in the Korean cohort. MATERIALS AND METHODS: In the global, randomized, observer-blind, placebo-controlled phase 3 trial (NCT04886596), adults ≥60 years of age were randomized 1:1 to receive a single intramuscular dose of the adjuvanted RSVPreF3 vaccine or placebo. The Korean cohort (12 sites) included 719 participants. Immunogenicity and reactogenicity were evaluated in a subset of participants. Safety data included solicited adverse events (AEs) within four days, unsolicited AEs up to 30 days, and serious adverse events (SAEs)/potential immune-mediated diseases up to six months post-vaccination. RESULTS: In the Korean cohort, 360 participants received the adjuvanted RSVPreF3 vaccine and 359 received placebo; 91 were included in the solicited safety set and 87 in the per-protocol immunogenicity set. By Day 31, neutralizing titers had increased robustly in the RSVPreF3 group with a mean geometric increase (MGI) versus baseline of 7.7 (RSV-A) and 7.2 (RSV-B); RSVPreF3-binding IgG concentrations showed an MGI of 13.4 in the RSVPreF3 group. Reactogenicity was mostly mild; solicited administration-site AEs occurred in 58.7% (predominantly pain) and solicited systemic AEs in 60.9% (predominantly fatigue) of participants in the RSVPreF3 group; no vaccine-related SAEs were reported. RSV-A and RSV-B neutralizing titers and RSVPreF3-binding IgG concentrations remained above baseline until 24 months post-vaccination, with an MGI of 2.2 (RSV-A), 1.3 (RSV-B), and 2.7 (RSVPreF3-binding IgG). CONCLUSION: In Korean adults aged ≥60 years, a single dose of the adjuvanted RSVPreF3 vaccine elicited a robust immune response, which persisted for up to 24 months post-vaccination, with an acceptable safety profile. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04886596.