What are the Canadian RSV (Respiratory Syncytial Virus) vaccination guidelines for high-risk infants, pregnant women, and the general population?

Canadian RSV Vaccination Guidelines

Primary Recommendation for Infants

Canada follows similar RSV prevention strategies to the United States, with two main options: maternal RSVpreF vaccination during pregnancy (32-36 weeks gestation) OR nirsevimab monoclonal antibody for infants, but both are not needed for most infants. 1, 2

Maternal Vaccination Strategy

Timing and Administration:

• Administer RSVpreF vaccine as a single 0.5 mL intramuscular dose between 32 weeks 0 days and 36 weeks 6 days of gestation 1
• Give during September through January in most continental regions to align with RSV season 1
• At least 14 days are required after maternal vaccination for adequate antibody development and transplacental transfer to protect the infant 1, 2

Efficacy Data:

• Prevents medically attended RSV-associated lower respiratory tract infection (LRTI) with 57.3% efficacy when given at 32-36 weeks 1
• Prevents severe RSV-associated LRTI with 76.5% efficacy 1
• Prevents RSV hospitalization with 48.2% efficacy 1

Safety Considerations:

• More preterm births were observed in vaccine recipients (5.7%) versus placebo (4.7%) during 24-36 weeks dosing, though not statistically significant 1
• More hypertensive disorders of pregnancy were observed in vaccine recipients, though not statistically significant 1
• FDA determined benefits outweigh risks when administered at 32-36 weeks gestation 1

Nirsevimab (Monoclonal Antibody) Strategy

Primary Indications:

• All infants <8 months born during or entering their first RSV season whose mother did not receive RSVpreF vaccine 1, 2
• All infants born at <34 weeks gestation regardless of maternal vaccination status 1, 2
• Infants born <14 days after maternal RSVpreF vaccination 1
• Infants whose mother's vaccination status is unknown 2

Dosing:

• 50 mg intramuscularly for infants weighing <5 kg 1
• 100 mg intramuscularly for infants weighing ≥5 kg 1
• Single dose provides protection for approximately 150 days 1

Efficacy Data:

• 79.0% efficacy in preventing medically attended RSV-associated LRTI 1
• 80.6% efficacy in preventing RSV-associated LRTI with hospitalization 1
• 90.0% efficacy in preventing RSV-associated LRTI with ICU admission 1

High-Risk Children in Second RSV Season:

• Children aged 8-19 months at increased risk for severe RSV disease entering their second RSV season should receive nirsevimab regardless of maternal vaccination 1

Special Populations Requiring Nirsevimab Despite Maternal Vaccination

Consider nirsevimab even if mother was vaccinated in rare circumstances:

• Infants born to immunocompromised mothers who may not have mounted adequate immune response 1, 2
• Infants born to mothers with conditions associated with reduced transplacental antibody transfer (e.g., HIV infection) 1
• Infants who underwent cardiopulmonary bypass or extracorporeal membrane oxygenation (may have lost maternal antibodies) 1
• Infants with substantially increased risk for severe RSV disease (hemodynamically significant congenital heart disease, chronic lung disease requiring medical intervention, or intensive care admission requiring oxygen at hospital discharge) 1

Palivizumab (Legacy Product)

Current Limited Role:

• Palivizumab is now recommended only for children with certain underlying medical conditions comprising <5% of all infants 1
• Use is further limited by high cost and requirement for monthly dosing 1
• Indicated for pediatric patients with history of premature birth (≤35 weeks gestational age) who are ≤6 months at beginning of RSV season, with bronchopulmonary dysplasia requiring medical treatment within previous 6 months who are ≤24 months, or with hemodynamically significant congenital heart disease who are ≤24 months 3
• Dose: 15 mg/kg intramuscularly monthly throughout RSV season 3
• Reduces RSV hospitalization by 45-55% 4

Critical Clinical Pitfalls to Avoid

Do NOT administer both maternal RSV vaccine AND infant nirsevimab for most infants - this dual approach is not needed and represents unnecessary intervention 1, 2

Do NOT give maternal RSV vaccine:

• Before 32 weeks or after 36 weeks 6 days gestation 1
• To pregnant persons with history of severe allergic reaction (anaphylaxis) to any vaccine component 1

Do NOT assume protection immediately:

• Infants born <14 days after maternal vaccination are not adequately protected and require nirsevimab 1
• The earliest an infant can be considered protected by maternal vaccination is if born at 34 weeks gestation when vaccine given at 32 weeks 2

Do NOT use palivizumab as first-line:

• Nirsevimab has replaced palivizumab for most indications due to single-dose convenience versus monthly injections 1

Seasonal Timing Considerations

For infants born outside RSV season (April-September):

• Mothers will not have been vaccinated during pregnancy 1
• Administer nirsevimab at onset of RSV season if infant is <8 months old 1

RSV season typically:

• Commences in November and lasts through April in northern hemisphere 3
• May begin earlier or persist later in certain communities 3