Protecting all infants against RSV in their first winter

Respiratory syncytial virus (RSV) is a common respiratory virus that causes infections ranging from mild cold-like illness to severe lung infections, including bronchiolitis and pneumonia. Although RSV affects all ages, hospitalisation rates are highest in young children and infants (particularly those <6 months). Research in Western Australia using linked laboratory test results and statistical modelling to account for untested cases, predicts that up to 1 in 30 infants under 6 months could be hospitalised for RSV. 

Fortunately, we are now in the era of RSV prevention for infants and young children with the maternal vaccine, Abrysvo® ,on the National Immunisation Program for pregnant women between 28 and 36 weeks, and infant immunisation with nirsevimab, Beyfortus®, supported through states and territories. Abrsvyo® works as an active vaccine where mums develop protective antibodies that are passed onto her child in utero. Beyfortus® is a long-acting monoclonal antibody providing direct protection to the infant from administration and can be given from birth to 2 years of age, depending on individual circumstances. Both products have been shown to be >80% effective in reducing RSV-hospitalisations in infants. Protection lasts approximately 6 months for both Absryvo® and Beyfortus®, with effectiveness gradually declining over time.

Navigating the complexity

RSV does not disappear after 6 months of age. Although the risk of severe infection is highest in early infancy, RSV-hospitalisations continue throughout early childhood. RSV is highly seasonal with hospitalisations peaking during periods of increased viral activity, typically over winter in temperate Australia. Consequently, age and timing of the RSV season are both important when considering protection against severe infection. 

The complexity of the RSV Maternal and Infant Protection Program, combined with the interplay between age and seasonality, can make it difficult for parents and carers to know how best to protect their child against RSV, ie which immunisation they or their child should have and when. For this reason, we developed the RSV Immunisation Guidance Tool, an interactive resource for parents, carers and healthcare professionals that provides tailored RSV immunisation guidance based on responses to a series of questions. At present, this tool is designed for WA. 

The role of age and season

From looking at >400,000 births linked to hospitalisation, laboratory and socio-demographic data, we wanted to see how season of birth influences patterns of RSV-hospitalisations during the first year of life. We found that summer-born infants in temperate Western Australia experience their highest RSV-hospitalisation rates between 5 and 8 months of age, while rates among spring-born infants peak between 8 and 10 months of age. These findings suggest maternal vaccination alone may leave a gap in protection against RSV-hospitalisations for some infants. This research forms part of our STAMP-RSV program — a holistic research program informing RSV public health policy. Our research suggests that offering Beyfortus to spring- and summer-born infants, regardless of maternal vaccination status, could prevent an average of 65 additional annual RSV-hospitalisations. That represents 65 fewer families avoiding the distress of having an infant in hospital with a serious chest infection. The WA Government used these findings to expand the current infant RSV immunisation program. 

This sequential immunisation approach, where maternal vaccination is followed by a monoclonal antibody for infants born well in advance of the traditional RSV season, aims to protect all infants throughout their first winter. To our knowledge, Western Australia is the only jurisdiction globally to implement this approach. Given the high effectiveness of both immunisation products, this has the potential to provide year-round protection and further reduce RSV-hospitalisations. We now need to know whether this message is reaching the community and being effectively communicated through health professional networks, and whether this approach could be expanded to other Australian jurisdictions. 

Looking to the future

Another monoclonal antibody, clesrovimab or Enflonsia®, has been licensed by the Therapeutic Goods Administration and is due for Pharmaceutical Benefits Advisory Committee consideration in November. This means Australia may soon have multiple monoclonal antibody options for RSV protection. Additionally, recent changes to the National Health Act 1953 allow monoclonal antibodies like Beyfortus® and Enflonsia® to be listed on the National Immunisation Program. This creates an opportunity for listing RSV immunisations in Baby Books, the parent-held child health record internationally recognised to provide clarity and improve uptake of prevention services like immunisation.  

Other Australian states and territories may look to Western Australia to see the impact of sequential RSV immunisation. To maximise protection for infants, we need to ensure families and healthcare providers are aware of the available immunisation options, ensuring uptake is high across all immunisation pathways.  

We are expanding our STAMP-RSV program nationally through an NHMRC-funded research program, RISE. We will address the need for easy-to-use resources helping community and providers navigate the complexities of RSV prevention. As part of this work, we plan to extend our RSV Immunisation Guidance Tool for use across Australia. 

Our research has highlighted the seasonal characteristics of RSV and the benefits of RSV immunisation, but also the challenges created by differing eligibility criteria and approaches across jurisdictions. We do not want infants to miss out on protection due to complexities and inconsistencies. A more consistent national approach, with clear and simple messaging, will ensure all infants can be protected against RSV and set our children up for lifelong lung health. 

Professor Hannah Moore OAM is an infectious disease epidemiologist and Theme Head, Infectious Diseases at The Kids Research Institute Australia with a joint appointment at the School of Population Health, Curtin University. 

Fiona Giannini is a mathematical modeller in the Infectious Disease Epidemiology team at The Kids Research Institute Australia and a PhD student at the National Centre for Epidemiology and Population Health, Australian National University.

Damien Foo is an epidemiologist in the Infectious Disease Epidemiology team at The Kids Research Institute Australia and a research fellow and biostatistician at the Faculty of Health Sciences, Curtin University.

Professor Paul Effler is a senior medical advisor in the WA Department of Health and adjunct faculty at the University of Western Australia.