A single dose of an experimental mRNA vaccine developed by Moderna has demonstrated significant efficacy against respiratory syncytial virus (RSV) in adults aged 60 years and older, according to data released in December 2023 and published in the New England Journal of Medicine. The vaccine, designated mRNA-1345, showed 83.7% efficacy in preventing RSV-associated lower respiratory tract disease with at least two signs or symptoms, and 82.4% efficacy against disease with at least three symptoms.
The randomized, double-blind, placebo-controlled phase 2-3 trial involved 35,541 participants, with 17,793 receiving the vaccine and 17,748 receiving a placebo. Participants had a median follow-up of 112 days, ranging from one to 379 days. The primary analyses were conducted after at least 50% of anticipated RSV-associated lower respiratory tract disease cases had occurred.
Researchers found that RSV-associated lower respiratory tract illness with at least two signs or symptoms occurred in 11 participants in the vaccine group (1.19 cases per 1000 person-years of observation) compared to 33 participants in the placebo group (3.58 cases per 1000 person-years of observation). The vaccine’s efficacy of 66.7% (with a 96.66% confidence interval of 28.8 to 85.8) in this category was a key finding. Even more pronounced was the efficacy against more severe illness, with only 2 cases (0.22 cases per 1000 person-years) occurring in the vaccine group versus 14 (1.52 cases per 1000 person-years) in the placebo group, representing an 85.7% efficacy (96.66% CI, 32.0 to 98.7).
The study also assessed the vaccine’s impact on RSV-associated acute respiratory illness, reporting a 62.1% efficacy (95% CI, 37.1 to 77.9) with 22 cases in the vaccine group (2.38 cases per 1000 person-years) and 58 cases in the placebo group (6.30 cases per 1000 person-years). According to the published data, the vaccine demonstrated no evident safety concerns.
A separate, interim analysis published in July 2022, and detailed in a study available through PubMed, showed similar trends in a slightly smaller cohort of participants (34,284 total, with 17,215 receiving the vaccine and 17,069 receiving a placebo). That analysis indicated a 66.7% vaccine efficacy against RSV-associated lower respiratory tract illness with at least two signs or symptoms.
The development of the mRNA-1345 vaccine builds on prior research demonstrating the immunogenicity and safety of the vaccine in both younger and older adults, with a phase 1 clinical trial showing the induction of neutralizing antibodies against both RSV A and B subtypes that persisted for at least six months. The ongoing ConquerRSV trial was initiated in November 2021 to further evaluate the vaccine’s safety and efficacy.
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