Peer-reviewed article
Comparing the potential impacts of seasonal immunisation against year-round immunisation to prevent RSV infant hospitalisations in Japan: A modelling study
Ayaka Monoi, Akira Endo, Matej Kriznar, Motoi Suzuki, Stefan Flasche ·
Summary
Written by AI, not yet AICS's view · claude-haiku-4-5-20251001This study models two immunisation strategies to prevent respiratory syncytial virus (RSV) hospitalisations in Japanese infants: year-round immunisation and seasonal immunisation timed to RSV circulation patterns. Using maternal vaccine and monoclonal antibody data, the researchers estimated that both approaches could substantially reduce RSV hospitalisations compared to current practice, with seasonal programmes achieving similar or slightly lower reductions depending on RSV predictability. The effectiveness of each strategy depends on how long protection lasts and how accurately RSV seasonality can be predicted.
Key points
- Year-round maternal vaccine (RSVpreF) could reduce RSV infant hospitalisations by 46% (95% UR: 31%, 65%)
- Year-round monoclonal antibody (nirsevimab) could reduce hospitalisations by 58% (95% UR: 39%, 79%)
- Seasonal and catch-up programmes achieved similar reductions: 52% (95% UR: 37%, 65%) for RSVpreF and 57% (95% UR: 38%, 75%) for nirsevimab
- If RSV seasonality is predictable, seasonal programmes could reduce hospitalisations by 56-61%, depending on the intervention
- Year-round programmes may be more effective if monoclonal antibody protection remains substantial beyond six months
Limitations
This is a modelling study using static cohort analysis, not an evaluation of actual immunisation programmes in practice. The findings depend on assumptions about RSV seasonality patterns, the duration of immunity from interventions, and the accuracy of underlying Japanese epidemiological data; real-world effectiveness may differ due to vaccination uptake, logistics, and changing RSV circulation patterns.
Abstract
The seasonal circulation of respiratory syncytial virus (RSV) in countries such as Japan, together with the transient nature of passive immunity conferred to infants via maternal vaccination or monoclonal antibody administration, may warrant a differential strategy for those born between the RSV seasons. Maximal effectiveness may be achieved by deferring immunisation of this cohort from birth until entry into their first RSV season using catch-up administration of monoclonal antibody through a seasonal and catch-up programme, compared with year-round administration. To estimate the benefit of seasonal and catch-up programmes in reducing RSV infant hospitalisations in Japan, we developed a static cohort model following infants through their first year of life, parameterised by Japanese data on weekly and municipality-specific RSV incidence during 2018 to 2025 and on RSV case hospitalisation risk from a health claims database study. We used Bayesian inference to estimate the effectiveness and its waning for maternal vaccine (RSVpreF) and long-acting monoclonal antibody (nirsevimab) from trial data. We estimate that year-round programme of RSVpreF or nirsevimab could reduce RSV hospitalisations from the status quo, under which only high-risk infants are eligible for monoclonal antibodies, by 46% (95% uncertainty range (UR): 31%, 65%) or 58% (95% UR: 39%, 79%), respectively. In comparison, the seasonal and catch-up programme could reduce by 52% (95% UR: 37%, 65%) or 57% (95% UR: 38%, 75%), respectively. If seasonality matches the seasonal immunisation timing, using 2024 as an example, the reduction by the seasonal and catch-up programme would be 56% (95% UR: 46%, 67%) or 61% (95% UR: 44%, 77%), respectively. If protection from nirsevimab remained substantial after six months, the year-round programme would likely to be more effective. RSVpreF and nirsevimab may substantially reduce RSV infant hospitalisations in Japan. The benefit of the seasonal programmes depends on predictability of RSV seasonality and potential logistical challenges.