A national hospital-based surveillance study from Australia found that the long-acting monoclonal antibody nirsevimab reduced respiratory syncytial virus (RSV)-related hospitalizations in infants under 12 months by over 80% during the country’s 2024 RSV season. The findings were published last week in Eurosurveillance.
Led by researchers from The Kids Research Institute Australia in Perth, the team analyzed data from nearly 4,000 children and adults hospitalized with RSV from April to December 2024 at 22 hospitals throughout Australia. Infants younger than 12 months accounted for nearly 40% of cases. Of all hospitalized patients, 6.6% required admission to intensive care or high-dependency units and of those, 6.1% were children.
Severe disease was most common among infants born prematurely, those with cardiac or neurologic conditions or genetic or metabolic disorders, and First Nations children. The in-hospital mortality rate was low (0.1%) among children, but reached 4.1% among adults.
Population-based vs risk-based approaches
In 2024, immunization strategies for young children across Australia varied by jurisdiction. Two states, Western Australia and Queensland, implemented population-wide infant immunization programs using nirsevimab. The rest of the country relied on targeted, risk-based vaccination programs.
In Western Australia and Queensland, nirsevimab effectiveness against RSV hospitalization in infants under 12 months was 83.1%. Western Australia saw a 50% reduction in hospitalized RSV cases in those younger than 12 months, and hospitalization rates fell by a similar amount in Queensland for those aged 6 months and younger. Total RSV cases in Western Australia and Queensland were significantly lower than in the rest of the country.
Despite some limitations, including reliance on self-reported information from some populations and the possibility of underreporting of immunization status, the findings “demonstrate the effectiveness of nirsevimab in jurisdictions providing population-wide programmes in 2024,” write the authors.