{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,4]],"date-time":"2026-10-04T12:26:14Z","timestamp":1791116774515,"version":"4.1.0"},"reference-count":23,"publisher":"American Medical Association (AMA)","issue":"10","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["JAMA Netw Open"],"abstract":"\n Importance<\/jats:title>\n New resistant mutations of respiratory syncytial virus type B (RSV-B) have been observed during the first year of implementation nirsevimab treatment. During the second season of implementation of nirsevimab treatment in France, RSV-B was predominant.<\/jats:p>\n <\/jats:sec>\n \n Objectives<\/jats:title>\n To assess and compare the effectiveness of nirsevimab treatment in preventing RSV bronchiolitis in pediatric emergency departments during the first and second seasons of implementation of treatment in France.<\/jats:p>\n <\/jats:sec>\n \n Design, Setting, and Participants<\/jats:title>\n This a multicenter test-negative case-control study included 636 infants younger than 1 year who received a diagnosis of a first bronchiolitis episode in 5 pediatric emergency departments in France during the 2 first seasons of implementation of nirsevimab treatment (from October 5, 2023, to February 29, 2024, and from October 15, 2024, to January 31, 2025) and underwent a nasopharyngeal test for RSV.<\/jats:p>\n <\/jats:sec>\n \n Main Outcomes and Measures<\/jats:title>\n The main outcome of the study was the RSV status of the bronchiolitis cases. Multivariable logistic regression was performed with nirsevimab as the explanatory variable, adjusted on age, sex, risk factors of bronchiolitis, type of childcare, month, and center of inclusion. Effectiveness was calculated for each season and compared using the likelihood ratio test. Subgroup analysis by age and severity as well as sensitivity analyses were performed.<\/jats:p>\n <\/jats:sec>\n \n Results<\/jats:title>\n \n The study included 636 patients with bronchiolitis (median age, 3.0 months [IQR, 1.4-5.0 months]; 333 boys [52.4%]). In both seasons, 162 of 636 patients (25.5%) were immunized with nirsevimab. During the first season of implementation, 273 of 384 patients (71.1%) tested positive for RSV; during the second season, 181 of 252 patients (71.8%) tested positive for RSV. The effectiveness of nirsevimab treatment against RSV bronchiolitis was estimated to be 83.2% (95% CI, 68.0%-91.4%) during the first season and 89.3% (95% CI, 77.8%-95.1%) during the second season; no statistically significant difference in effectiveness was found between the 2 seasons (\n P<\/jats:italic>\n \u2009=\u2009.97). Subgroup and sensitivity analyses provided similar results.\n <\/jats:p>\n <\/jats:sec>\n \n Conclusions and Relevance<\/jats:title>\n In this test-negative case-control study of nirsevimab treatment, its effectiveness in reducing pediatric emergency department visits for RSV bronchiolitis during the second season of national immunization was high and comparable with that observed in the first season. Although RSV-B resistant strains had been recently identified, it did not appear to have important clinical consequences to date. Continued close monitoring of RSV epidemiology in the context of the widespread nirsevimab use remains essential.<\/jats:p>\n <\/jats:sec>","DOI":"10.1001\/jamanetworkopen.2025.40720","type":"journal-article","created":{"date-parts":[[2025,10,30]],"date-time":"2025-10-30T15:31:35Z","timestamp":1761838295000},"page":"e2540720","source":"Crossref","is-referenced-by-count":6,"title":["Nirsevimab Treatment of RSV Bronchiolitis in Pediatric Emergency Departments"],"prefix":"10.1001","volume":"8","author":[{"given":"Lea","family":"Lenglart","sequence":"first","affiliation":[{"name":"Pediatric Emergency Department, Robert Debr\u00e9 Hospital, Assistance Publique\u2013H\u00f4pitaux de Paris, Paris, France"},{"name":"Infection, Antimicrobials, Modelling, Evolution, INSERM UMR 1137, Paris Cit\u00e9 University, Paris, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Corinne","family":"Levy","sequence":"additional","affiliation":[{"name":"Association Clinique et Th\u00e9rapeutique Infantile du Val de Marne, Cr\u00e9teil, France"},{"name":"Universit\u00e9 Paris Est, IMRB-GRC GEMINI, Cr\u00e9teil, France"},{"name":"Clinical Research Center, Centre Hospitalier Intercommunal de Cr\u00e9teil, Cr\u00e9teil, France"},{"name":"Groupe de Pathologie Infectieuse P\u00e9diatrique, Paris, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Romain","family":"Basmaci","sequence":"additional","affiliation":[{"name":"Infection, Antimicrobials, Modelling, Evolution, INSERM UMR 1137, Paris Cit\u00e9 University, Paris, France"},{"name":"Groupe de Pathologie Infectieuse P\u00e9diatrique, Paris, France"},{"name":"Pediatric Emergency Department, Louis Mourier Hospital, Assistance Publique\u2013H\u00f4pitaux de Paris, Paris, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Karine","family":"Levieux","sequence":"additional","affiliation":[{"name":"Pediatric Emergency Department, Nantes University Hospital, Nantes, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rolf","family":"Kramer","sequence":"additional","affiliation":[{"name":"Sanofi Pasteur, Lyon, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pauline","family":"De Mari","sequence":"additional","affiliation":[{"name":"Sanofi Pasteur, Lyon, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"St\u00e9phane","family":"B\u00e9chet","sequence":"additional","affiliation":[{"name":"Association Clinique et Th\u00e9rapeutique Infantile du Val de Marne, Cr\u00e9teil, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Elise","family":"Launay","sequence":"additional","affiliation":[{"name":"Groupe de Pathologie Infectieuse P\u00e9diatrique, Paris, France"},{"name":"Department of Pediatrics, Nantes University Hospital, Nantes, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lise Martin","family":"Perceval","sequence":"additional","affiliation":[{"name":"Department of Pediatrics, Nantes University Hospital, Nantes, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Laure","family":"Cohen","sequence":"additional","affiliation":[{"name":"Pediatric Emergency Department, Louis Mourier Hospital, Assistance Publique\u2013H\u00f4pitaux de Paris, Paris, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Camille","family":"Aupiais","sequence":"additional","affiliation":[{"name":"Groupe de Pathologie Infectieuse P\u00e9diatrique, Paris, France"},{"name":"Department of Pediatrics, Jean Verdier Hospital, Assistance Publique\u2013H\u00f4pitaux de Paris, Paris, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Loic","family":"de Pontual","sequence":"additional","affiliation":[{"name":"Groupe de Pathologie Infectieuse P\u00e9diatrique, Paris, France"},{"name":"Department of Pediatrics, Jean Verdier Hospital, Assistance Publique\u2013H\u00f4pitaux de Paris, Paris, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alexis","family":"Rybak","sequence":"additional","affiliation":[{"name":"Association Clinique et Th\u00e9rapeutique Infantile du Val de Marne, Cr\u00e9teil, France"},{"name":"Groupe de Pathologie Infectieuse P\u00e9diatrique, Paris, France"},{"name":"Department of Pediatrics, Department Woman-Mother-Child, Lausanne University Hospital (Centre Hospitalier Universitaire Vaudois), Lausanne, Vaud, Switzerland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Naim","family":"Ouldali","sequence":"additional","affiliation":[{"name":"Infection, Antimicrobials, Modelling, Evolution, INSERM UMR 1137, Paris Cit\u00e9 University, Paris, France"},{"name":"Groupe de Pathologie Infectieuse P\u00e9diatrique, Paris, France"},{"name":"Department of General Pediatrics, Pediatric Infectious Disease and Internal Medicine, Robert Debr\u00e9 University Hospital, 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Haute Autorit\u00e9 de Sant\u00e9. September 14, 2023. Accessed April 1, 2024. https:\/\/www.has-sante.fr\/upload\/docs\/application\/pdf\/2023-09\/reponse_rapide__nirsevimab_beyfortus.pdf"},{"key":"zoi251114r13","unstructured":"RSV subtypes dashboard. GISAID.org. Accessed January 23, 2025. https:\/\/gisaid.org\/rsv-subtypes-dashboard\/"},{"key":"zoi251114r17","unstructured":"Infections respiratoires aigu\u00ebs (grippe, bronchiolite, COVID-19): bulletin du 27 mars 2024. Sant\u00e9 Publique France. Accessed March 28, 2024. https:\/\/www.santepubliquefrance.fr\/maladies-et-traumatismes\/maladies-et-infections-respiratoires\/grippe\/documents\/bulletin-national\/infections-respiratoires-aigues-grippe-bronchiolite-covid-19-.-bulletin-du-27-mars-2024"},{"key":"zoi251114r18","unstructured":"Infections respiratoires aigu\u00ebs (grippe, bronchiolite, COVID-19): bulletin du 5 f\u00e9vrier 2025. Sant\u00e9 Publique France. 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