HealthDay News — Healthy late-preterm and term infants who receive a single injection of nirsevimab administered before the respiratory syncytial virus (RSV) season are protected from medically attended RSV-associated lower respiratory tract infection, according to a study published in the New England Journal of Medicine.

Laura L. Hammitt, MD, from Johns Hopkins University in Baltimore, and colleagues randomly assigned infants who were born at a gestational age of at least 35 weeks to receive a single intramuscular injection of nirsevimab or placebo before the start of an RSV season. A total of 1490 infants were randomly assigned: 994 to the nirsevimab group and 496 to the placebo group.

The researchers found that medically attended RSV-associated respiratory tract infection occurred in 1.2% and 5.0% of infants in the nirsevimab and placebo groups, respectively, corresponding to 74.5% efficacy for nirsevimab. Hospitalization for RSV-associated lower respiratory tract infection occurred in 0.6% and 1.6% of infants in the nirsevimab and placebo groups, respectively (efficacy, 62.1%). Antidrug antibodies after baseline were detected in 6.1% and 1.1% of infants with data available to day 361 in the nirsevimab and placebo groups, respectively. Serious adverse events were reported in 6.8% and 7.3% of those who received nirsevimab and placebo, respectively.


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“The results were consistent with those from a trial involving preterm infants that showed that the incidence of medically attended RSV-associated lower respiratory tract infection was 70.1% lower (95% confidence interval, 52.3 to 81.2) with nirsevimab prophylaxis than with placebo,” the authors write.

The study was funded by MedImmune/AstraZeneca and Sanofi; Sanofi is developing nirsevimab with AstraZeneca.

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