Abstract
Respiratory syncytial virus (RSV) is a major respiratory pathogen that particularly affects infants under 6 months, premature infants, and those with congenital heart disease (CHD) or chronic lung disease. In 2019, there was estimated 3.6 million hospital admissions among children under 5 years of age due to RSV-related lower respiratory tract infection (RSV-LRTI), with more than 26,000 deaths. For decades, monthly palivizumab injection has provided passive immunization for high-risk infants and has demonstrated efficacy in reducing RSV-related hospitalizations, while breastfeeding has been known to protect against severe RSV-LRTI. Recent advances aiming to reduce severe RSV-LRTI, that is, bronchiolitis and pneumonia, include maternal RSV immunization and long-acting monoclonal antibodies for infants. Bivalent non-adjuvanted RSV vaccine (Abrysvo®), RSVPreF, administered during pregnancy (gestational age 24–36 weeks) transfers protective RSV IgG antibodies across the placenta with high cord-to-maternal ratio at ~1.5. Studies have shown that maternal immunization significantly reduced medically attended severe RSV-associated LRTI in infants, with an efficacy of 81.8% at 90 days and 69.4% at 180 days after birth, respectively. For medically attended RSV-associated LRTI, the efficacy was 57.1% at 90 days and 51.3% at 180 days. Additionally, long-acting RSV monoclonal antibodies (Nirsevimab) provide season-long protection with a single dose for infants during the first RSV season, reducing both medically attended RSV-LRTI and hospitalizations by approximately 70%–80% in infants during their first RSV season. Consequently, in 2024, the Strategic Advisory Group of Experts (SAGE) recommended that countries introduce maternal RSVPreF vaccination and/or RSV monoclonal antibodies for infant RSV prevention. Many countries have already adopted these interventions, demonstrating cost-effectiveness of monoclonal antibodies.