Current Challenges and Future Directions for RSV Prevention Strategies in Japan.

Respiratory syncytial virus (RSV) remains a leading cause of lower respiratory tract infections in infants, particularly those under 6 months of age. In Japan, RSV seasonality in temperate regions has recently shifted from traditional winter peaks to more year-round circulation, with this change most pronounced in higher latitude areas such as Hokkaido, where outbreaks increasingly peak in summer. Japan has recently approved 2 RSV prevention tools: nirsevimab for infants and a maternal vaccine. However, challenges remain: maternal vaccines require out-of-pocket payment, and nirsevimab is reimbursed only for high-risk infants under national insurance and must be administered during the RSV season. These limitations call for policy and system-level improvements to ensure equitable access. A season-independent, risk-based prevention strategy-such as maternal vaccination at or after 28 weeks' gestation and nirsevimab for preterm or otherwise unvaccinated infants-may help optimize protection while minimizing overlap. Adapting implementation strategies to Japan's shifting epidemiology will be essential to efficiently protect all infants. Japan's experience may also provide insights for other countries facing changes in RSV transmission patterns and planning broader prevention approaches.