MSD：ENFLONSIAClesrovimab approved for marketing in China.

On June 11, the NMPA official website showed that Merck’s Clesrovimab (MK-1654) Injection has been approved for marketing in China. The indication is for the prevention of lower respiratory tract infection caused by respiratory syncytial virus (RSV) in neonates and infants entering or born during their first RSV season.

RSV is a contagious virus that causes widespread seasonal infections. Clesrovimab is a prophylactic long-acting monoclonal antibody that induces passive immunity against RSV by binding to the RSV fusion glycoprotein, thereby preventing RSV infection. It is designed to provide direct, rapid, and durable protection for infants.

In June 2025, Clesrovimab was approved for marketing by the U.S. FDA, becoming the first and only single-dose RSV monoclonal antibody for infants, regardless of patient weight.

In January 2021, Merck initiated a IIb/III, double-blind, randomized, placebo-controlled study, CLEVER (MK-1654-004), to evaluate the efficacy and safety of Clesrovimab for protection in healthy preterm and full-term infants. The trial met its primary endpoint and key secondary endpoints.

Compared with placebo, by Day 150 (5 months) post-dosing, the Clesrovimab group showed a 60.5% reduction in the incidence of medically attended RSV-related lower respiratory tract infection (MALRI) (95% CI: 44.2, 72.0; p<0.001) and an 84.3% reduction in RSV-related hospitalization rates (95% CI: 66.7, 92.6; p<0.001). For infants entering their first RSV season, the safety profile of Clesrovimab was generally comparable to placebo. The most common adverse reactions included injection site erythema within 5 days post-dosing, injection site swelling within 5 days post-dosing, and rash within 14 days post-dosing.

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