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# Merck sBLA for Expanded Use of RSV Therapy
- URL: https://www.fdaweb.com/merck-sbla-for-expanded-use-of-rsv-therapy/
- Published: 2026-08-06T12:00:00.000Z
- Updated: 2026-09-14T13:44:36.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5161593

FDA has accepted for review a Merck supplemental BLA for Enflonsia (clesrovimab-cfor) to expand its indication to include preventing respiratory syncytial virus (RSV) lower respiratory tract disease (LRTD) in children under age two years at increased risk for severe RSV disease through their second RSV season. The agency has set a user fee review action target date of 3/22/2027.

Enflonsia was originally [approved by FDA](https://cts.businesswire.com/ct/CT?id=smartlink&url=https%3A%2F%2Fwww.merck.com%2Fnews%2Fu-s-fda-approves-mercks-enflonsia-clesrovimab-cfor-for-prevention-of-respiratory-syncytial-virus-rsv-lower-respiratory-tract-disease-in-infants-born-during-or-entering-their-fir%2F&esheet=54584018&newsitemid=20260805331090&lan=en-US&anchor=approved+by+the+U.S.+FDA&index=1&md5=88d207d071fcba231a1fd3451ae2a827&ref=fdaweb.com) 6/2025 for preventing RSV LRTD in infants born during or entering their first RSV season. “Even with protection during their first RSV season, certain children – including those born with chronic lung disease, congenital heart disease or early or moderate preterm birth with certain risk conditions – remain vulnerable to severe RSV disease during their second RSV season,” Merck says.

Enflonsia is described as a half-life monoclonal antibody (mAb) that is administered using the same dose regardless of weight. It is designed to provide direct, rapid and durable protection through 5 months, a typical RSV season, according to the company. For infants born during the RSV season, it is to be administered within the first week of life, it says. For infants born outside of the RSV season, it should be administered shortly before the RSV season begins.