Presentation (CTI)

OBJECTIVES: An ongoing, phase 2/3, randomised, double-blind, placebo-controlled study evaluating a single dose of mRNA-1345 (50μg) demonstrated sustained vaccine efficacy (VE) in preventing the first episode of RSV-associated lower respiratory tract disease (LRTD) with ≥2 symptoms over a 24-month period (median follow-up: 18.8 months) in adults aged ≥60 years. This analysis aimed to estimate the VE of mRNA-1345 over a 60-month time-horizon using a model-based approach.
METHODS: A non-linear model was fitted to monthly calculated vaccine efficacy of mRNA-1345 through a median follow-up of 18.8 months. The model used the logarithm of time as the independent variable and monthly log incidence rate ratio (log-IRR) as the dependent variable. This model was then used to estimate the monthly VE against RSV-LRTD with ≥2 symptoms and acute respiratory disease (ARD). VE from month 2 post-vaccination are estimated using this model, allowing for development of immunity during month 1.
RESULTS: Modelled VE against RSV-LRTD was estimated to be 76.9% in the second month post-vaccination, declining to 39.1% by Month 24. Beyond 24 months, the rate of waning slowed, with VE projected at 31.0%, 24.7%, and 19.4% at Months 36, 48, and 60, respectively (Figure 1). Similarly, modelled VE against RSV-ARD was estimated to peak at 69.2% in Month 2 and declined to 44.9% by Month 24, with slower waning thereafter. Projected VE was 28.7%, 23.7%, and 19.6% at Months 36, 48, and 60, respectively (Figure 2).
CONCLUSIONS: This non-linear modelling analysis over a 60-month time horizon suggests that a single dose of mRNA-1345 may provide ongoing protection against RSV associated LRTD and ARD beyond 24 months. Furthermore these results, alongside real-world data, can also help to inform policymakers about the optimal timing and need for RSV revaccination in adults.