December 22, 2024

Early Estimate of Nirsevimab Effectiveness for Prevention of Respiratory Syncytial Virus–Associated Hospitalization Among Infants Entering Their First Respiratory Syncytial Virus Season

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Early Estimate of Nirsevimab Effectiveness for Prevention of Respiratory Syncytial Virus–Associated Hospitalization Among Infants Entering Their First Respiratory Syncytial Virus Season

A recent study has found that nirsevimab, a medication aimed at preventing severe respiratory syncytial virus (RSV) disease in infants, was shown to be 90% effective in preventing RSV-associated hospitalization during their first RSV season.

The multisite analysis included 699 infants who were hospitalized with acute respiratory infection (ARI), and it was found that nirsevimab was effective at a median of 45 days from receipt to the onset of ARI symptoms. These early effectiveness estimates align with current recommendations for preventing severe RSV disease in infants during their first season.

While the study had strengths such as systematic RSV testing and verification of nirsevimab receipt for all infants, it is important to note that effectiveness may decrease over the full RSV season as antibody levels wane. The Centers for Disease Control and Prevention (CDC) will continue to monitor nirsevimab effectiveness under real-world conditions throughout the RSV season, especially in high-risk children aged 8-19 months.

Limitations of the study include the limited availability of nirsevimab in the first season and the possibility of RSV infections occurring before the infants received the medication. Additionally, the study did not assess nirsevimab effectiveness by dosage or against outcomes such as outpatient and emergency department visits, indicating the need for further research in these areas.

The findings of the study support current CDC recommendations for maternal RSV vaccination or infant receipt of nirsevimab to reduce the risk of RSV-associated hospitalization in infants during their first RSV season. This research highlights the importance of effective prevention strategies for RSV in infants, especially during their first season.

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