The U.S. Food and Drug Administration on Monday approved Merck's preventive antibody shot to protect infants up to one year of age from respiratory syncytial virus during their first RSV season, the company said.

The United States has seen limited supply of Sanofi and AstraZeneca's antibody Beyfortus, the only preventive shot for RSV available for infants and toddlers so far.

Merck's therapy, called clesrovimab and branded as Enflonsia, is a monoclonal antibody that can be administered as a single dose regardless of birth weight in healthy pre-term, full-term and at-risk infants to protect them against mild, moderate and severe RSV.

RSV is a common respiratory virus that causes seasonal infections such as the flu, but is a leading cause of pneumonia and death in infants and older adults.

Each year in the United States, an estimated 58,000–80,000 children younger than five years are hospitalized due to RSV, according to the U.S. Centers for Disease Control and Prevention.

The CDC currently recommends two immunization options for babies to be protected from severe RSV — an RSV vaccine given to the mother during pregnancy or an RSV antibody given to the baby.

Merck expects the drug's shipments to arrive in time for the 2025-2026 RSV season.

The CDC's Advisory Committee on Immunization Practices is expected to meet later this month to discuss and make recommendations for the use of Enflonsia in infants.