To the Editor—I read the article by Hon et al1 with interest. Although the seasonality of respiratory syncytial virus (RSV) is mostly year-round in tropical and subtropical regions, this should not be a barrier to universal maternal RSV vaccination.2 This approach could work well in Hong Kong, as unlike the monoclonals, the RSV vaccine’s effects are designed to be longer-lasting, and all pregnant women are eligible. In contrast to its much more restricted predecessor, palivizumab, nirsevimab has fewer limitations and can be given to all newborns, providing protection against RSV for up to 5 months after a single dose. Due to its more limited duration of protection, the recommendation is for it to be administered just before the onset of the RSV season (eg, during September/October to March in the Northern Hemisphere).2 3 Nirsevimab can still be given to particularly vulnerable babies following maternal vaccination, especially when vaccination occurs within 14 days of delivery since the maternal vaccine response can take up to 2 weeks to develop.3 In addition, the United States Centers for Disease Control and Prevention recommends that non-vulnerable babies above 8 months of age should not receive nirsevimab, and it is not recommended for any baby over 20 months.3 Nonetheless, the optimal scheduling, combination and effectiveness of these two interventions (RSV vaccines vs monoclonals) clearly require further experience. In the meantime, recommendations from different countries can be confusing, and the local teams in Hong Kong may find it useful to wait a little longer before developing their own local guidelines. Therefore, I agree with the authors that no new practice recommendations should be made at this time regarding RSV vaccines or the long-acting monoclonal nirsevimab.

The author contributed to the letter and critical revision of the letter for important intellectual content. The author had full access to the data, contributed to the study, approved the final version for publication, and takes responsibility for its accuracy and integrity.

The author has disclosed no conflicts of interest.

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1. Hon KL, Cheung EW, Li AM, et al. Practice recommendations for respiratory syncytial virus prophylaxis among children in Hong Kong. Hong Kong Med J 2025;31:48-57. Crossref

2. Benzaken TR, Watson C, Drysdale SB. Prevention of respiratory syncytial virus disease by immunisation. Arch Dis Child Educ Pract Ed 2024:edpract-2024-326964. Crossref

3. US Centers for Disease Control and Prevention. RSV Immunization Guidance for Infants and Young Children. 30 Aug 2024. Available from: https://www.cdc.gov/rsv/hcp/vaccine-clinical-guidance/infants-young-children.html. Accessed 25 Feb 2025.