information For healthcare providers
RSV Protection: Side Effects & Safety
Like all medicines and vaccines, RSV protection options can cause side effects. Not everyone will experience them, and most side effects are mild and get better on their own. Serious side effects are rare but can happen. This page provides a clinically relevant summary of adverse events, contraindications, and safety considerations associated with the currently authorized infant RSV protection options in Canada. This material presents a balanced overview of both benefits and risks associated with RSV prevention strategies, but it does not replace the full Product Monographs.
Healthcare professionals are encouraged to review the complete Product Monograph and NACI recommendations prior to prescribing, administering, or counselling patients.
Infant RSV Immunizations: Protection through Monoclonal Antibodies
- Nirsevimab (Beyfortus®) Product monograph
- Clesrovimab (ENFLONSIA®) Product Monograph
Therapeutic classification: Long-acting monoclonal antibodies targeting the RSV prefusion F protein.
Health Canada Indications:
- Authorized for the prevention of RSV lower respiratory tract disease in Neonates and infants entering or during their first RSV season
- Authorized for children up to 24 months of age who remain vulnerable to severe RSV disease through their second RSV season, which may include, but is not limited to, children with:
- Chronic lung disease of prematurity (CLD)
- Hemodynamically significant congenital heart disease (CHD)
- Immunocompromised states
- Down syndrome
- Cystic fibrosis
- Neuromuscular disease
- Congenital airway anomalies
- Authorized for the prevention of RSV lower respiratory tract disease in neonates and infants who are born during or entering their first RSV season.
Mechanism of action: Nirsevimab and clesrovimab are long-acting monoclonal antibodies directed against the RSV prefusion F protein. They provide passive immunity by neutralizing viral entry and preventing viral replication in host cells.
Adverse Reactions
Commonly reported adverse reactions for both infant immunizations:
- Injection-site reactions (pain, erythema, swelling, induration)
- Rash
- Fever
Rare but serious adverse reactions:
- Hypersensitivity reactions (including anaphylaxis)
- Anaphylaxis has been observed with human immunoglobulin G1 (IgG1) monoclonal antibodies.
Contraindications
Beyfortus® Nirsevimab (Beyfortus®): Infants with a history of severe hypersensitivity reactions, including anaphylaxis, to this drug or to any ingredients in the formulation, including any non-medicinal ingredient, or component of the container.
ENFLONSIA® Clesrovimab (ENFLONSIA®): Infants with a history of serious hypersensitivity reactions, including anaphylaxis, to any component or ingredient of the product.
Precautions
- Use caution in infants with a history of severe allergic conditions; risk of serious hypersensitivity reactions, including anaphylaxis
- Emergency treatment and appropriate medical supervision for anaphylaxis must be immediately available in the event of an anaphylactic reaction
- Immunization may not provide the same level of protection in individuals with protein-losing conditions
- Not indicated for adults, pregnant or breastfeeding individuals.
Special populations
- Safety and efficacy data in preterm infants demonstrate protective benefits but warrant careful monitoring due to clinical vulnerability.
- Data in infants with severe immunocompromise or chronic respiratory disease are limited; risk-benefit should be assessed individually.
Beyfortus® Nirsevimab (Beyfortus®): Authorized for selected children who remain vulnerable to severe RSV disease during a second RSV season.
ENFLONSIA® Clesrovimab (ENFLONSIA®): Authorized for first RSV season. NACI’s current recommendations may be consulted separately for recommended timing and programmatic guidance, which may differ from the authorized indication, such as immunization to be considered for off-label use for infants and children at ongoing risk in their second RSV season based on current evidence of immunogenicity and safety. Consult the current Canadian product monograph and NACI guidance for more information.
Healthcare providers should report suspected adverse reactions through the adverse events following immunization (AEFI) reporting form.
RSV Vaccine for Pregnant People
Therapeutic classification: Bivalent stabilized pre-fusion F subunit vaccine
Health Canada Indication for infant RSV protection: Active immunization of pregnant individuals between 32 and 36 weeks’ gestation to prevent RSV-associated lower respiratory tract disease in infants from birth through 6 months of age. NACI’s current recommendations may be consulted separately for recommended timing and programmatic guidance, which may differ from the authorized indication. Consult the current Canadian product monograph and NACI guidance for more information.
Mechanism of action: Induces maternal RSV-neutralizing antibodies that cross the placenta via FcRn-mediated transfer, conferring passive immunity to the newborn.
Adverse Reactions
Commonly reported reactions:
- Injection-site reactions (pain, erythema, swelling, induration)
- Headache
- Muscle pain (myalgia)
Severe (rare) reactions:
- Hypersensitivity reactions, including anaphylaxis
Note: Healthcare providers should consult the current Product Monograph for complete prescribing and safety information.
Healthcare providers should report suspected adverse reactions through the adverse events following immunization (AEFI) reporting form.
Use During Pregnancy
Clinical studies and post-market surveillance continue to support the safety profile of RSVpreF vaccination during pregnancy. Healthcare providers should consult the current Product Monograph and current NACI guidance for complete prescribing and safety information.
Contraindications:
- Individuals who are hypersensitive to the active substance (RSV subgroup A Stabilized Prefusion F protein antigen and RSV subgroup B Stabilized Prefusion F protein antigen) or to any component of the vaccine
- History of severe allergic reaction to a previous RSVpreF dose
Precautions & Warnings:
- Defer vaccination in individuals with acute febrile illness.
- Assess prior history of severe allergic reaction to vaccines or injectable biologics.
- Pregnancy-specific risk assessment should include obstetric history, gestational age verification and concurrent medical conditions.
- Immunocompromised individuals (there is limited data; may have diminished immune response)
- Breastfeeding individuals (there is limited data)