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Background: The mRNA-1345 vaccine demonstrated efficacy against respiratory syncytial virus (RSV) disease with acceptable safety in adults aged ≥60 years in the ConquerRSV trial. Here, humoral immunogenicity results from the trial are presented., Methods: This phase 2/3 trial randomly assigned adults (≥60 years) to mRNA-1345 50-µg encoding prefusion F (preF) glycoprotein (n = 17 793) vaccine or placebo (n = 17 748). RSV-A and RSV-B neutralizing antibody (nAb) and preF binding antibody (bAb) levels at baseline and day 29 postvaccination were assessed in a per-protocol immunogenicity subset (PPIS; mRNA-1345, n = 1515; placebo, n = 333)., Results: Day 29 nAb geometric mean titers (GMTs) increased 8.4-fold against RSV-A and 5.1-fold against RSV-B from baseline. Seroresponses (4-fold rise from baseline) in the mRNA-1345 groups were 74.2% and 56.5% for RSV-A and RSV-B, respectively. Baseline GMTs were lower among participants who met the seroresponse criteria than those who did not. mRNA-1345 induced preF bAbs at day 29, with a pattern similar to nAbs. Day 29 antibody responses across demographic and risk subgroups were generally consistent with the overall PPIS., Conclusions: mRNA-1345 enhanced RSV-A and RSV-B nAbs and preF bAbs in adults (≥60 years) across various subgroups, including those at risk for severe disease, consistent with its demonstrated efficacy in the prevention of RSV disease., Clinical Trials Registration: NCT05127434., Competing Interests: Potential conflicts of interest. G. P. M. reports funding from Moderna, Merck, Sanofi, Pfizer, Universidad Nacional de San Martín, Medicago, GSK, and Cassara. C. J. A. D. reports receiving grants from the Medical Research Council and Wellcome, a consultancy for Synarigen, and is a member of the data and safety monitoring board at Oxford University. J. G., L. L., J. D., A. K., S. M., W. H., H. Z., S. K. S., F. P., N. L., C. A. S., E. W., J. M. M., and R. D. are employees of Moderna, Inc., and may hold stock/stock options in the company. N. L. C., K. S., and J. E. T. are consultants for Moderna, Inc. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2024. Published by Oxford University Press on behalf of Infectious Diseases Society of America.)

Background: Respiratory syncytial virus (RSV) presents a global health concern. A lipid nanoparticle-encapsulated mRNA-based RSV vaccine (mRNA-1345) that encodes the membrane-anchored RSV prefusion-stabilized F glycoprotein is under clinical investigation., Methods: This phase 1 dose escalation study was based on a randomized, observer-blind, placebo-controlled design, and it assessed the safety and immunogenicity of mRNA-1345 in healthy adults aged 18 to 49 years. Participants were randomized to receive 1 dose of mRNA-1345 (50, 100, or 200 µg) or placebo or 3 doses of mRNA-1345 (100 µg) or placebo 56 days apart., Results: mRNA-1345 was well tolerated at all dose levels. The most common solicited adverse reactions were pain, headache, fatigue, myalgia, or chills, which were all generally mild to moderate. At 1 month postinjection, a single injection of mRNA-1345 boosted RSV neutralizing antibody titers (geometric mean fold rise: RSV-A, 20.0-23.5; RSV-B, 11.7-16.0) and RSV prefusion binding antibody concentrations (geometric mean fold rise, 16.1-21.8), with no apparent dose response. Antibody levels remained above baseline through 6 months. Sequential doses of 100 µg were well tolerated but did not further boost antibody levels., Conclusions: A single mRNA-1345 injection demonstrated an acceptable safety profile in younger adults and induced a durable neutralizing antibody response, supporting its continued development., Clinical Trials Registration: ClinicalTrials.gov NCT04528719., Competing Interests: Potential conflicts of interest. C. A. S., R. M., A. K., R. D., L. W., L. E. A., S. S.-G., K. S., and S. K. S. are employees of Moderna, Inc, and may hold stock/stock options in the company. A. A. and G. L. C. were Moderna, Inc, employees at the time of study conduct. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2024. Published by Oxford University Press on behalf of Infectious Diseases Society of America.)

Background: An mRNA-based respiratory syncytial virus (RSV) vaccine, mRNA-1345, is under clinical investigation to address RSV disease burden in older adults., Methods: Based on a randomized, observer-blind, placebo-controlled design, this phase 1 dose-ranging study evaluated the safety, reactogenicity, and immunogenicity of mRNA-1345 in adults aged 65 to 79 years. Participants were randomized to receive 1 dose of mRNA-1345 (12.5, 25, 50, 100, or 200 µg) or placebo and matched mRNA-1345 booster or placebo at 12 months., Results: Overall, 298 participants received the first injection and 247 received the 12-month booster injection. mRNA-1345 was generally well tolerated after both injections, with the most frequently reported solicited adverse reactions being injection site pain, fatigue, headache, arthralgia, and myalgia. Reactogenicity was higher after the booster injection but with severity, time to onset, and duration similar to the first injection. A single mRNA-1345 injection boosted RSV-A and RSV-B neutralizing antibody titers and prefusion F binding antibody (preF bAb) concentrations at 1 month (geometric mean fold rises: RSV-A, 10.2-16.5; RSV-B, 5.3-12.5; preF bAb, 7.2-12.1). RSV antibody levels remained above baseline through 12 months, indicating immune persistence. A 12-month booster injection also increased RSV-A and RSV-B neutralizing antibody titers and preF bAb concentrations; titers after booster injection were numerically lower than those after the first dose, with overlapping 95% CIs., Conclusions: mRNA-1345 was well tolerated and immunogenic following a single injection and a 12-month booster., Clinical Trials Registration: NCT04528719 (ClinicalTrials.gov)., Competing Interests: Potential conflicts of interest. C. A. S., R. M., A. K., R. D., L. W., C. A. P., J. G., E. W., R. G., A. K. S., C. R., S. K. S., and G. L. C. are employees of Moderna, Inc, and may hold stock/stock options in the company. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2024. Published by Oxford University Press on behalf of Infectious Diseases Society of America.)

Background: Respiratory syncytial virus (RSV) is a common cause of lower respiratory tract infections in infants. This phase 1/2, observer-blind, randomized, controlled study assessed the safety and immunogenicity of an investigational chimpanzee-derived adenoviral vector RSV vaccine (ChAd155-RSV, expressing RSV F, N, and M2-1) in infants., Methods: Healthy 6- to 7-month-olds were 1:1:1-randomized to receive 1 low ChAd155-RSV dose (1.5 × 1010 viral particles) followed by placebo (RSV_1D); 2 high ChAd155-RSV doses (5 × 1010 viral particles) (RSV_2D); or active comparator vaccines/placebo (comparator) on days 1 and 31. Follow-up lasted approximately 2 years., Results: Two hundred one infants were vaccinated (RSV_1D: 65; RSV_2D: 71; comparator: 65); 159 were RSV-seronaive at baseline. Most solicited and unsolicited adverse events after ChAd155-RSV occurred at similar or lower rates than after active comparators. In infants who developed RSV infection, there was no evidence of vaccine-associated enhanced respiratory disease (VAERD). RSV-A neutralizing titers and RSV F-binding antibody concentrations were higher post-ChAd155-RSV than postcomparator at days 31, 61, and end of RSV season 1 (mean follow-up, 7 months). High-dose ChAd155-RSV induced stronger responses than low-dose, with further increases post-dose 2., Conclusions: ChAd155-RSV administered to 6- to 7-month-olds had a reactogenicity/safety profile like other childhood vaccines, showed no evidence of VAERD, and induced a humoral immune response. Clinical Trials Registration. NCT03636906., Competing Interests: Potential conflicts of interest. V. N., Y. Z., W. P., D. F., I. D., A. G. L., R. M., S. K. S., and N. V. are or were employees of GSK during the conduct of the study. I. D., W. P., and S. K. S. hold GSK shares/stocks. R. M. and S. K. S. hold stock/stock options in Moderna. B. T., E. J. A., B. S. C., E. C. D., H. S., J. D. C., J. M. M. A., K. L., M. M. M.-P., M. R., S. N. F., F. B.-A., and T. P. report grants and/or other support from GSK for the conduct of the study. J. M. L. reports grants from GSK paid to her institution for the conduct of the study and holds the CIHR-GSK Chair in Pediatric Vaccinology at Dalhousie University. B. T. reports grants from GSK, Merck, and Pfizer for other trials. C. e. reports support for scientific meetings from GSK and ViiV and advisory consultancy fees from GSK. E. J. A. has consulted for Pfizer, Sanofi Pasteur, GSK, Janssen, Moderna, and Medscape, and his institution receives funds to conduct clinical research unrelated to this manuscript from MedImmune, Regeneron, PaxVax, Pfizer, GSK, Merck, Novavax, Sanofi Pasteur, Janssen, and Micron; he serves on a safety monitoring board for Kentucky BioProcessing and Sanofi Pasteur; serves on a data adjudication board for WCG and ACI Clinical; and his institution has also received funding from the National Institutes of Health to conduct clinical trials of COVID-19 vaccines. B. S. C. reports grants for other vaccine trials from GSK and MSD paid to his institution. E. C. D. performs contract work for the Eskisehir Osmangazi University funded by GSK, Sanofi Pasteur, and Pfizer. E. K. reports honoraria for lectures from GSK, MSD, AstraZeneca, Sanofi, and Pfizer. E. L.-M. reports grants from Centro de Estudios en Infectología Pediátrica. F. M.-T. reports grants from Janssen, MSD, and AstraZeneca; personal fees from Ablynx, GSK, Pfizer, MSD, Sanofi Pasteur, Novavax, Seqirus, and Biofabri; nonfinancial support from GSK, Pfizer, MSD, and Seqirus; and trial fees paid to his institution from these different companies (except Biofabri). H. S. reports personal fees and trial fees paid to his institution from MSD, Seqirus, Pfizer, Janssen, and Sanofi Pasteur. I. S. C. has received payment to his institution from GSK for the conduct of the study, by contract approved by the corresponding ethical committees and health authorities, and for trials of other vaccine manufacturers, and has received grants and/or honoraria as a consultant/advisor/speaker or for attending conferences and practical courses from GSK and other vaccine manufacturers. J. D. C. is a member of the Committee on Infectious Diseases of the American Academy of Pediatrics and reports funds paid to his university to study RSV vaccines. J. D.-D. reports grants from GSK, MSD, and Sanofi Pasteur paid to his institution. J. M. M. A. reports fees for medical meetings from GSK and Pfizer. K. L. reports grants from ReViral and Shionogi. M. M.-P. reports grants from MSD, Roche, GSK, Janssen, Takeda, and Syneos. M. R. reports grants for other vaccine trials from GSK and other vaccine manufacturers paid to his institution. S. N. F. reports fees paid to his institution for attending meetings, advisory boards, and/or grants for clinical trials from AstraZeneca/Medimmune, GSK, J&J, Pfizer, Sanofi, Seqirus, Sandoz, Valneva, Novavax, and Merck. X. S.-L. reports grants from Cevaxin Vaccine Research Center. F. B.-A. reports consultancy fees from GSK, Pfizer, and MSD and grants from MSD. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America.)

Background: Respiratory syncytial virus (RSV) can cause substantial morbidity and mortality among older adults. An mRNA-based RSV vaccine, mRNA-1345, encoding the stabilized RSV prefusion F glycoprotein, is under clinical investigation., Methods: In this ongoing, randomized, double-blind, placebo-controlled, phase 2-3 trial, we randomly assigned, in a 1:1 ratio, adults 60 years of age or older to receive one dose of mRNA-1345 (50 μg) or placebo. The two primary efficacy end points were the prevention of RSV-associated lower respiratory tract disease with at least two signs or symptoms and with at least three signs or symptoms. A key secondary efficacy end point was the prevention of RSV-associated acute respiratory disease. Safety was also assessed., Results: Overall, 35,541 participants were assigned to receive the mRNA-1345 vaccine (17,793 participants) or placebo (17,748). The median follow-up was 112 days (range, 1 to 379). The primary analyses were conducted when at least 50% of the anticipated cases of RSV-associated lower respiratory tract disease had occurred. Vaccine efficacy was 83.7% (95.88% confidence interval [CI], 66.0 to 92.2) against RSV-associated lower respiratory tract disease with at least two signs or symptoms and 82.4% (96.36% CI, 34.8 to 95.3) against the disease with at least three signs or symptoms. Vaccine efficacy was 68.4% (95% CI, 50.9 to 79.7) against RSV-associated acute respiratory disease. Protection was observed against both RSV subtypes (A and B) and was generally consistent across subgroups defined according to age and coexisting conditions. Participants in the mRNA-1345 group had a higher incidence than those in the placebo group of solicited local adverse reactions (58.7% vs. 16.2%) and of systemic adverse reactions (47.7% vs. 32.9%); most reactions were mild to moderate in severity and were transient. Serious adverse events occurred in 2.8% of the participants in each trial group., Conclusions: A single dose of the mRNA-1345 vaccine resulted in no evident safety concerns and led to a lower incidence of RSV-associated lower respiratory tract disease and of RSV-associated acute respiratory disease than placebo among adults 60 years of age or older. (Funded by Moderna; ConquerRSV ClinicalTrials.gov number, NCT05127434.)., (Copyright © 2023 Massachusetts Medical Society.)