Safety, Tolerability, and Immunogenicity of the mRNA-1345 RSV Vaccine in Solid Organ Transplant Recipients Aged ≥18 Years

Document Type

Conference Proceeding

Publication Date

1-11-2026

Publication Title

Open Forum Infect Dis

Keywords

mRNA-1345, mycophenolate mofetil, mycophenolic acid, neutralizing antibody, respiratory syncytial virus vaccine, steroid, tacrolimus, adult, adverse drug reaction, conference abstract, drug combination, female, follow up, graft recipient, human, Human respiratory syncytial virus, immunogenicity, immunosuppressive treatment, major clinical study, male, phase 3 clinical trial, randomized controlled trial, side effect, single drug dose, vulnerable population

Abstract

Background: Solid organ transplant recipients (SOTRs) are at increased risk for severe respiratory syncytial virus (RSV) disease due to chronic immunosuppression. Interim safety and immunogenicity are presented from a phase 3 trial evaluating 2 mRNA-1345 doses in SOTRs ≥18 years. Methods: An ongoing, open-label, phase 3 trial (NCT06067230) evaluated 2 mRNA-1345 50-μg doses, 56 days apart, in adults ≥18 years with liver, kidney, or lung transplant ≥180 days prior to the study. Primary objectives included safety, tolerability, and immunogenicity assessed by RSV-A and -B neutralizing antibodies (nAbs). Primary objective included measurement of geometric mean titers (GMTs) on Day 85; secondary objective included measurement of GMTs on Day 29. Results: Of 150 SOTR (50 kidney, 52 liver, and 48 lung), 146 received both doses. Median follow-up from Dose 1 was 223 days (range 8-335). Median age was 57 years (range 24-80), 37.3% were female, and 26.7% received SOT < 2 years prior. Most participants (80.6%) were taking concomitant tacrolimus ± mycophenolate ± steroids. Solicited adverse reactions (SARs) within 7 days were similar after both doses (local: 74.0%, 77.4%; systemic: 64.0%, 64.4%; Fig. 1). No grade 4 local SARs, adverse events (AEs) leading to study/vaccine discontinuation, deaths, or AEs of special interest were reported. One month after Dose 1, RSV-A nAbs rose 4.9-fold from baseline; 1 month after Dose 2, nAbs rose 7.1-fold from baseline (Fig. 2). RSV-B nAb response had a 3.4-fold increase from baseline after Dose 1, and a 5.2-fold increase after Dose 2. Titers achieved varied by SOT type. Liver SOTR titers after Dose 1 were comparable to those observed in non-immunocompromised adults in the pivotal efficacy trial . GMTs were lower in kidney and lung SOTRs, SOTRs < 2 years post-transplant, and those on mycophenolate mofetil (MMF), but increased after Dose 2 (Fig. 3). Conclusion: Two doses of mRNA-1345 50-μg administered 56 days apart in SOTRs were well-tolerated, with no safety concerns. A single dose was immunogenic across all SOTR groups, and a second dose boosted responses, especially in kidney SOTRs, lung SOTRs, those < 2 years post-transplant, or on MMF; therefore, mRNA-1345 is likely to be effective in this vulnerable population.

Volume

13

First Page

S55

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