• Laura L Hammitt, Ron Dagan, Yuan Yuan, Manuel Baca Cots, Miroslava Bosheva, Shabir A Madhi, William J Muller, Heather J Zar, Dennis Brooks, Amy Grenham, Ulrika Wählby Hamrén, Vaishali S Mankad, Pin Ren, Therese Takas, Michael E Abram, Amanda Leach, M Pamela Griffin, Tonya Villafana, and MELODY Study Group.
• From the Department of International Health, Johns Hopkins University, Baltimore (L.L.H.), and AstraZeneca, Gaithersburg (Y.Y., D.B., A.G., P.R., T.T., M.E.A., A.L., M.P.G., T.V.) - both in Maryland; the Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel (R.D.); Quirónsalud Málaga Hospital, Malaga, Spain (M.B.C.); University Multiprofile Hospital for Active Treatment, St. George Medical University, Plovdiv, Bulgaria (M.B.); the South African Medical Research Council Vaccines and Infectious Diseases Analytics Research Unit and African Leadership in Vaccinology Expertise, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg (S.A.M.), and the Department of Paediatrics and Child Health, Red Cross Children's Hospital, and the Medical Research Council Unit on Child and Adolescent Health, University of Cape Town, Cape Town (H.J.Z.) - all in South Africa; Ann and Robert H. Lurie Children's Hospital of Chicago and Northwestern University Feinberg School of Medicine, Chicago (W.J.M.); AstraZeneca, Gothenburg, Sweden (U.W.H.); and AstraZeneca, Durham, NC (V.S.M.).
• N. Engl. J. Med. 2022 Mar 3; 386 (9): 837-846.

BackgroundRespiratory syncytial virus (RSV) is a major cause of lower respiratory tract infection and hospitalization in infants. Nirsevimab is a monoclonal antibody to the RSV fusion protein that has an extended half-life. The efficacy and safety of nirsevimab in healthy late-preterm and term infants are uncertain.MethodsWe randomly assigned, in a 2:1 ratio, infants who had been 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. The primary efficacy end point was medically attended RSV-associated lower respiratory tract infection through 150 days after the injection. The secondary efficacy end point was hospitalization for RSV-associated lower respiratory tract infection through 150 days after the injection.ResultsA total of 1490 infants underwent randomization: 994 were assigned to the nirsevimab group and 496 to the placebo group. Medically attended RSV-associated lower respiratory tract infection occurred in 12 infants (1.2%) in the nirsevimab group and in 25 infants (5.0%) in the placebo group; these findings correspond to an efficacy of 74.5% (95% confidence interval [CI], 49.6 to 87.1; P<0.001) for nirsevimab. Hospitalization for RSV-associated lower respiratory tract infection occurred in 6 infants (0.6%) in the nirsevimab group and in 8 infants (1.6%) in the placebo group (efficacy, 62.1%; 95% CI, -8.6 to 86.8; P = 0.07). Among infants with data available to day 361, antidrug antibodies after baseline were detected in 58 of 951 (6.1%) in the nirsevimab group and in 5 of 473 (1.1%) in the placebo group. Serious adverse events were reported in 67 of 987 infants (6.8%) who received nirsevimab and in 36 of 491 infants (7.3%) who received placebo.ConclusionsA single injection of nirsevimab administered before the RSV season protected healthy late-preterm and term infants from medically attended RSV-associated lower respiratory tract infection. (Funded by MedImmune/AstraZeneca and Sanofi; MELODY ClinicalTrials.gov number, NCT03979313.).Copyright © 2022 Massachusetts Medical Society.

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