Every year, Canadian hospitals brace for the RSV season, a time when the tiniest patients—infants and young children—are particularly vulnerable. For healthcare professionals, understanding and mitigating the impact of Respiratory Syncytial Virus (RSV) in this population is crucial. 

RSV is not just another virus; it’s a pervasive threat that infects nearly all children by the age of two. Despite its prevalence, many parents and even some clinicians underestimate its potential severity. 

In this guide, we’ll explore the burden of RSV in infants, identify risk factors for severe infection, and summarize the National Advisory Committee on Immunization (NACI) guidance for a universal RSV immunization program.

Understanding RSV’s Impact on Infants

RSV is a single-stranded, negative-strand RNA virus belonging to the family Paramyxoviridae and genus Pneumovirus. The virus’s ability to cause bronchiolitis and pneumonia makes it particularly dangerous for infants and young children. Each year, RSV leads to numerous hospitalizations, highlighting the need for effective prevention and treatment strategies.

Despite its high infectivity, many cases of RSV may go unnoticed or be misdiagnosed, especially in milder cases. In Canada, RSV represents a significant healthcare burden, particularly during peak seasons. The virus’s ability to spread rapidly in communities underscores the importance of early detection and prevention. 

Risk Factors for Severe RSV Infection

While RSV can affect any child, certain risk factors increase the likelihood of severe infection. One of the most notable risk factors is chronic lung disease, such as bronchopulmonary dysplasia, which compromises an infant’s respiratory function and increases susceptibility to severe RSV outcomes.

Additional risk factors include those born preterm and low birth weight, particularly for infants currently weighing less than 5 kg (11 lbs). Immune compromise, whether due to conditions like severe combined immunodeficiency or medical treatments that suppress the immune system, also heightens the risk of severe RSV. Exposure to tobacco smoke in utero can impair lung development, further increasing vulnerability. Socioeconomic factors, including limited access to healthcare and crowded living conditions, exacerbate the risks, making early intervention and education vital.

The Role of RSV Immunoprophylaxis in Disease Prevention

In the fight against RSV, immunoprophylaxis plays a critical role in preventing severe disease. Active immunization involves the body’s inherent production of antibodies against a specific agent after exposure to the antigen through vaccination. These active immunizing agents, commonly referred to as vaccines, foster long-term immunity by stimulating the body’s defense mechanisms.

Conversely, passive immunization provides immediate, temporary protection by transferring preformed antibodies. This can occur naturally, by maternal-fetal antibody transfer, or through systemic administration of monoclonal antibodies. 

Palivizumab, a monoclonal antibody for RSV immunoprophylaxis, has been a licensed option for over 20 years. Its authorization covers high-risk pediatric patients up to 24 months who are vulnerable to RSV complications. However, its high cost and monthly administration requirements limit its use to those with the highest risk profiles.

Despite its effectiveness in reducing hospitalizations, palivizumab does not prevent RSV infection entirely. Therefore, it should be part of a comprehensive strategy that includes infection control measures, such as hand hygiene and minimizing exposure to sick contacts.

New Developments in RSV Protection: Nirsevimab and RSVpref 

The advent of two new immunization products, nirsevimab and RSVpreF, marks significant progress in passive immunity options. 

Nirsevimab, a long-acting monoclonal antibody, represents a new frontier in RSV immunoprophylaxis. Authorized by Health Canada to protect all infants during their first RSV season and those vulnerable in their second season, nirsevimab offers broader coverage compared to palivizumab. 

Unlike palivizumab, nirsevimab requires only a single dose per season, simplifying administration for families and healthcare providers. 

RSVpreF leverages the concept of maternal immunization. It’s administered to pregnant individuals between 32-36 weeks gestational age, resulting in the passive transfer of antibodies to the fetus. By generating a robust maternal antibody response, RSVpreF protects infants during their first RSV season, a critical period of vulnerability. Educating expectant mothers about the benefits of RSVpreF and incorporating it into routine prenatal care can enhance uptake and protect the youngest patients from the outset.

Navigating the Latest NACI Guidelines

The National Advisory Committee on Immunization (NACI) released updated guidelines emphasizing the importance of RSV prevention in infants. They advocate for a universal immunization program, recommending nirsevimab as the preferred product due to its higher efficacy and longer duration of protection.

Programs can build and expand over time depending on access to supply, cost-effectiveness, and affordability of available options. 

Nirsevimab should be prioritized for infants in the following way:

Priority 1:

• Infants entering, or born during, their first RSV season who are at increased risk of severe RSV disease, including those who are born at less than 37 weeks gestational age.
• Infants entering their second RSV season and at ongoing increased risk of severe RSV disease.
• Infants entering, or born during, their first RSV season whose transportation for severe RSV disease treatment is complex, and/or whose risk of severe RSV disease intersects with established social and structural health determinants such as those experienced by some Indigenous communities across First Nations, Métis and Inuit populations.

Priority 2: 

• If nirsevimab is priced in a manner to make such programs cost-effective, NACI recommends nirsevimab be considered for any infant less than 8 months of age entering, or born during, their first RSV season through universal immunization programs to prevent severe RSV disease. 

NACI recommends RSVpreF may be considered as an individual decision by a pregnant woman or pregnant person together with information from their pregnancy care provider, in advance of, or during, the RSV season, to prevent severe RSV disease in their infant. 

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RSV poses a significant threat to infants and young children, but recent advancements in prevention offer hope for reducing its impact. By understanding the burden of RSV, identifying risk factors, and building towards a universal RSV immunization program, healthcare professionals can protect vulnerable populations and improve outcomes. 

Stay current and keep your patients safe: browse our range of resources on the latest NACI guidance for RSV and infants, including a 15-min Expert Brief, and one-hour CME.