Merck reports RSV antibody study success

Merck & Co. announced promising results for its experimental drug, clesrovimab, developed to protect infants from respiratory syncytial virus (RSV). The drug, an antibody, successfully achieved its primary safety and efficacy goals in a large, late-stage trial involving over 3,600 healthy or preterm infants. The trial was placebo-controlled, and the objectives included measuring the incidence of RSV-related lower respiratory infections needing medical attention over five months and monitoring certain adverse events.

A Merck spokesperson reported that clesrovimab also met a significant secondary goal by reducing the risk of hospitalization due to RSV. However, detailed results from the study have not yet been disclosed and will be presented at an upcoming medical meeting. Meanwhile, Merck plans to submit the data to global health authorities.

Clesrovimab is a critical part of Merck’s pipeline, especially as the company faces the upcoming expiration of key patents for its top-selling cancer drug, Keytruda. Merck has highlighted clesrovimab, along with other promising treatments like the pulmonary arterial hypertension drug Winrevair, which has already reached the market and is projected to achieve multibillion-dollar sales. Merck's research chief, Dean Li, has expressed optimism about clesrovimab, emphasizing its potential to distinguish itself in the competitive market for RSV therapies.

The treatment landscape for RSV has changed considerably, with three vaccines and an antibody drug called Beyfortus becoming available since last year. Beyfortus, also designed to protect infants from RSV, saw substantial sales last fall, a period when RSV infections typically surge. GSK's vaccine, Arexvy, generated $1.5 billion in 2023, and Sanofi and AstraZeneca's Beyfortus earned around $594 million, with expectations to exceed $1 billion in sales this year.

Jefferies analyst Peter Welford pointed out that Beyfortus has set a high efficacy standard for clesrovimab. Beyfortus demonstrated a 70% and 75% reduction in medically attended lower respiratory tract disease in two studies, an 83% reduction in preventing hospitalizations in a larger trial, and an 82% risk reduction in real-world use according to a study published in The Lancet.

Merck executives argue that clesrovimab may have an edge due to its lower likelihood of promoting viral resistance and its administration via a single fixed dose, unlike Beyfortus, which requires two injections. In early-stage trials, clesrovimab showed a similar risk reduction for lower respiratory tract infections. Nevertheless, Welford noted that clesrovimab would need to exhibit an 80% to 90% reduction in hospitalizations to match Beyfortus's performance.

Merck has yet to provide a specific timeline for releasing the detailed findings from the clesrovimab study.