Statement on the prevention of respiratory syncytial virus (RSV) disease in infants

What 

Respiratory syncytial virus (RSV) is one of the most common respiratory viruses in infants and young children, infecting almost all children by the age of 2 years old. RSV can cause serious respiratory disease in infants, young children and older adults. RSV has a seasonal pattern of activity where infections are usually more common in the winter with variation in the timing and magnitude of the peak. 

This statement focuses on the protection of infants and children from RSV disease. Health Canada has recently authorized two immunization products, both based on the pre-fusion stabilized F protein from RSV (RSVpreF), to protect infants from RSV using passive immunity: 

• Nirsevimab (BEYFORTUSTM, Sanofi) is a monoclonal antibody authorized with an indication to directly protect all infants in their first RSV season and children who remain vulnerable to severe RSV disease in their second RSV season. 
• RSVpreF (ABRYSVOTM, Pfizer) is a vaccine authorized with an indication to protect infants in their first RSV season through the passive transfer of maternal antibodies to the fetus by active immunization of a pregnant woman or pregnant person. 

Who 

Severe RSV disease is most common in young infants in their first months of life. Although the risk of severe RSV disease is higher in infants with certain medical conditions including prematurity (List 1), term infants account for the highest number of infants with severe RSV disease. Infants with certain medical conditions (List 1) remain at risk for severe RSV disease during their second RSV season. The limited data currently available indicate that pregnancy does not appear to increase the risk of severe RSV disease in pregnant women or pregnant people. Immunization of this group though leads to maternal antibodies that cross the placenta and provide passive protection against severe RSV disease for the infant after birth. Immunization in pregnancy can therefore be used to protect the infant. Considering the significant burden of disease in all infants from RSV and the impacts of RSV on the Canadian health system, NACI recommends building towards a universal RSV immunization program for all infants. Currently, nirsevimab is preferred over RSVpreF. Program introduction could occur in stages depending on access to supply, cost-effectiveness, and affordability of available options. NACI recommends RSV immunization programs use nirsevimab to prevent severe RSV disease. 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 (wGA) (List 1). 
• Infants entering their second RSV season and at ongoing increased risk of severe RSV disease (List 1).
• 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. At the present time, NACI does not recommend an immunization program for RSVpreF. More data and information are expected to emerge over time and NACI will reconsider this recommendation in the future.