Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory infections in young children worldwide. In 2019, RSV was responsible for an estimated 33 million RSV-associated acute lower respiratory infection episodes, 3.6 million hospital admissions, and 101 400 deaths in children under aged under 5 years worldwide, with more than 97% of these deaths occurring in low-income and middle-income countries (LMICs).1 In the United States, an estimated 58 000 to 80 000 young children are hospitalized with RSV annually, with the highest incidence in infants aged under 6 months.2 The economic burden for RSV-associated infections is substantial. Primary medical costs exceed $700 million annually in the United States, and secondary costs such as parental work loss and long-term respiratory sequelae add significantly to the overall impact.3,4 RSV infection in infancy has been linked to an increased risk of recurrent wheezing and asthma, highlighting that the impact of these infections extends beyond the initial illness.5
Given the widespread severity of RSV, implementing effective prevention strategies is vital. However, the path to RSV prevention has been defined by both scientific breakthroughs and sobering setbacks. The field was fundamentally shaped by the antibody-mediated enhancement observed in a 1960s vaccine trial, in which a formalin-inactivated RSV vaccine led to increased disease severity upon natural infection in vaccinated children.6,7 This tragic outcome halted vaccine development for decades, prompting a cautious, immunology-driven approach to future RSV interventions. In the 1990s, the development of palivizumab, the first monoclonal antibody targeting RSV, represented a significant advancement in RSV prevention.8 However, monthly dosing, high cost, and restricted eligibility criteria limited its impact, leaving most infants unprotected.9 Given these limitations, there remained a need for a more accessible, scalable solution that targeted all infants. This was especially important, since the vast majority of infants and young children hospitalized with RSV, including those admitted to the intensive care unit, are otherwise healthy prior to becoming infected with this virus.
The approval of nirsevimab, a long-acting RSV monoclonal antibody, in 2023 marked a transformative moment in RSV prevention. It offers single-dose seasonal protection with broad eligibility and improved feasibility for widespread use.10 In the same year, maternal RSV vaccination became available, providing an additional prevention strategy through transplacental antibody transfer, offering newborns protection at birth.11
Both strategies have demonstrated high efficacy in preventing severe RSV illness,12,13 with additional support from real-world effectiveness studies.14 However, successful implementation is key to achieving their full benefits. The COVID-19 pandemic has reshaped the landscape of vaccine acceptance, with parents expressing hesitancy toward newly introduced vaccines.15–17 The growing influence of social media misinformation, declining trust in public health institutions, and health care provider burnout further contribute to challenges in uptake.18 Beyond vaccine acceptance, disparities in health care access further complicate implementation. Factors such as insurance coverage, provider availability, and geographic barriers also create potential gaps in protection.19 Implementation science offers valuable frameworks for overcoming these challenges by emphasizing strategies that address system-, provider-, and patient-level barriers.
Findings from the Irving et al study20 in this issue of Pediatrics provide a crucial early assessment of RSV immunization coverage in the United States following the 2023 recommendations for maternal RSV vaccination and infant nirsevimab administration. The study aimed to assess the proportion of infants immunized against RSV through either antenatal vaccination or postnatal receipt of nirsevimab administration among linked pregnancy-infant dyads. Using electronic health records and immunization registry data from 10 Vaccine Safety Datalink health systems, the researchers identified pregnant individuals aged 12 to 55 years who gave birth to live infants of at least 32 weeks’ gestation between September 22, 2023, and March 31, 2024. RSV immunization was defined as either maternal vaccination at least 14 days before birth or nirsevimab receipt after birth. The study leveraged a validated pregnancy identification algorithm to link pregnancies with their corresponding infant records, enabling a comprehensive assessment of real-world immunization coverage. The primary endpoint of the study was the overall proportion of infants immunized against RSV through either intervention. To identify potential disparities in coverage, researchers stratified immunization frequency by race, ethnicity, birth month, and maternal age as well as by patterns of nirsevimab administration timing, which varied based on when infants received the immunization. For example, 58.2% received nirsevimab in the first week of life, whereas later administration was less common, especially for those born in January through March 2024.
Among 36 949 linked pregnancy-infant dyads, 72% of infants were immunized against RSV using either intervention, representing an encouraging level of early adoption. However, the study also revealed significant racial and ethnic disparities in coverage. Immunization rates were highest among infants born to non-Hispanic Asian mothers (84%) but dropped to 60% among infants born to non-Hispanic Black and non-Hispanic Middle Eastern or North African mothers. Additionally, coverage varied by birth month, ranging from 59% in September 2023 to 78% in January 2024, likely reflecting shifts in product availability and clinical practice patterns over time. Nirsevimab was more frequently administered to infants born earlier in the RSV season, whereas maternal vaccination became the predominant source of protection for infants born later in the season. This pattern aligns with the timing of the maternal vaccine rollout and the temporary nirsevimab supply constraints. Encouragingly, providers largely adhered to Advisory Committee on Immunization Practices recommendations regarding maternal RSV vaccination timing (32–36 weeks’ gestation) and the administration of nirsevimab to infants born within 14 days of maternal vaccination.
Irving et al’s study provides an assessment of RSV immunization efforts in select US medical centers, offering valuable insights into early adoption trends, potential access barriers, and coverage disparities by demographic characteristics by leveraging large-scale linked datasets. The study found high overall uptake in the first year of implementation but identified disparities in coverage by race, maternal age, and birth timing. This study’s robust methodology and ability to capture population-level trends offer an important reference point for future studies and policy decisions. However, further studies are needed to evaluate product effectiveness, identify barriers to equitable uptake, and optimize strategies for sustained implementation.
Given that most RSV-associated deaths occur outside the United States, global efforts to scale up RSV prevention should prioritize equitable access, particularly in LMICs and other resource-limited settings. While international organizations such as Gavi the Vaccine Alliance, the World Health Organization, and United Nations Children’s Fund are exploring financing strategies to support widespread adoption, significant challenges remain in pricing, supply chain logistics, and health care infrastructure capacity.21 Implementation efforts must be tailored to local contexts, balancing cost-effectiveness considerations with public health priorities. Pediatricians play a critical role in these efforts by advocating for equitable RSV immunization policies, educating families about the benefits of maternal vaccination and monoclonal antibodies, and supporting their integration into routine immunization programs. Their engagement in global health initiatives, research collaborations, and policy discussions can help drive sustainable solutions, ensuring long-term accessibility and uptake worldwide.
We are at a defining moment in RSV prevention. For the first time, we have the tools to significantly reduce RSV morbidity and mortality through maternal vaccination and monoclonal antibody prophylaxis. Yet, scientific innovation alone is not enough. Successful implementation will require strategic policymaking, effective communication, and a commitment to equity. By applying lessons from past vaccine rollouts, investing in community trust, and addressing barriers to access, we can maximize the impact of these life-saving interventions. The opportunity before us is unprecedented, and with coordinated global efforts, RSV prevention can become a reality for all infants, regardless of geography or socioeconomic status.
Dr Hayek contributed to the conceptualization of the commentary, drafted the original commentary, and contributed to the review and editing process. Dr Gailani contributed to the conceptualization of the commentary and participated in the review and editing of the commentary. Dr Halasa contributed to the conceptualization of the commentary, supervised the work, and participated in the review and editing of the manuscript. All authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work.
CONFLICT OF INTEREST DISCLOSURES: Dr Halasa received grant support from Sanofi and Quidel, reports a current investigator-initiated grant from Merck, and serves on an advisory board for CSL Seqirus. The other authors report no other disclosures.
COMPANION PAPER: A companion to this article can be found online at www.pediatrics.org/cgi/doi/10.1542/peds.2024-070240.
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