Nirsevimab in a single intramuscular dose prevents medically attended RSV infection and hospitalization in preterm infants

Reference

Griffin MP, Yuan Y, Takas T, et al. Single-dose nirsevimab for prevention of RSV in preterm infants. N Engl J Med 2020;383(5):415-425.

Synopsis

RSV is a common infection in infants, and preterm infants have a higher risk of severe illness. Nirsevimab is a monoclonal antibody with a long half-life allowing it to be given in a single dose, rather than given monthly, as is the currently approved drug Synagis. This study recruited healthy preterm infants born between 29 weeks and 34 weeks, 6 days of gestational age who were younger than 1 year at the beginning of the "RSV season" that typically runs from October through April in the United States (see https://www.cdc.gov/surveillance/nrevss/rsv/region.html for regional RSV surveillance for RSV in the United States). The mean age of infants was 3.3 months, with only 14% older than 6 months, and a mean weight of 4.5 kg. The investigators excluded infants who met the criteria for RSV prophlaxis, were acutely ill at the time of randomization, or had received another RSV-specific monoclonal antibody. A total of 1453 infants were randomized in a 2:1 ratio to receive nirsevimab 50 mg or placebo intramuscular injection. Groups were balanced at baseline, and analysis was by intention to treat, but there is no mention of concealment of allocation. Patients were recruited from both northern and southern hemispheres. The primary outcome of medically attended, PCR-confirmed RSV infection in either inpatient or outpatient setting in the 150 days following enrollment was less likely in the intervention group (2.6% vs 9.5%; P < .001; NNT = 14). Hospitalization for RSV infection was also less common in the intervention group (0.8% vs 4.1%; P < .001; NNT = 30). There were 2 deaths in the nirsevimab group and 3 deaths in the placebo group, unrelated to treatment of RSV. Both overall and serious adverse events were similar between groups, though 5 placebo group patients (vs 0 nirsevimab patients) went to the intensive care unit, 4 of whom required assisted ventilation.