Merck’s Clesrovimab shows promise as new RSV fighter for infants

USA—American multinational Merck has announced promising safety and efficacy results from a phase 2/3 clinical trial of clesrovimab (MK-1654-004), a monoclonal antibody developed to protect infants from respiratory syncytial virus (RSV) infection.

The trial involved more than 3,600 healthy or preterm infants and met its primary safety and efficacy endpoints, including significant reductions in medically attended lower respiratory infections caused by RSV through day 150.

The success of this late-stage trial is notable, as it included goals such as the incidence of RSV-associated lower respiratory infections requiring medical attention over five months compared to a placebo, and the percentage of patients experiencing specific adverse events.

Merck plans to present detailed findings at an upcoming scientific congress and will file the data with global regulatory authorities.

Merck is exploring Clesrovimab as a potential replacement for Keytruda, which will lose its patent protection by 2030. The drug is administered in a single, fixed-dose injection.

In her statement , Dr. Paula Annunziato, senior vice president of infectious diseases and vaccines at Merck Research Laboratories, emphasized the significance of RSV as a highly contagious virus that can cause severe respiratory issues in infants, leading to hospitalization.

She expressed optimism about the trial results and looks forward to collaborating with regulators to provide a new option to mitigate the impact of RSV on infants and their families.

RSV is a seasonal virus that poses a substantial burden on infants and older adults worldwide.

There is a high unmet need for preventative options for both healthy and high-risk infants, as RSV is the leading cause of hospitalization for healthy infants under a year old.

The virus can lead to serious respiratory conditions such as bronchiolitis and pneumonia, causing an estimated 101,000 deaths annually in children under five.

If approved by federal regulators, clesrovimab would become the second prophylactic monoclonal antibody injection available for infants against RSV.

 In July 2023, the Food and Drug Administration (FDA) approved the first such preventive measure for infants, nirsevimab-alip (Beyfortus), developed by AstraZeneca.

However, unprecedented demand for Beyfortus last fall and winter led to supply shortages, motivating Merck to join the effort.

Sales of RSV preventive products surged last fall when seasonal infections peaked. For instance, GSK’s vaccine, Arexvy, generated US$1.5 billion in 2023.

Sanofi and AstraZeneca faced higher-than-anticipated demand for Beyfortus, which earned approximately US$594 million in 2023. It is projected to surpass US$1 billion in sales this year.

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