Oct 17 (Reuters) - Merck ( MRK ) said on Thursday its

experimental antibody therapy, clesrovimab, demonstrated a 60.4%

effectiveness in reducing some types of respiratory syncytial

virus (RSV)-associated infections in infants.

The seasonal shot met its primary goal in the mid-to-late

stage trial, reducing the incidence of RSV-associated, medically

attended lower respiratory infections in healthy infants up to

one year old entering their first RSV season.

The drug also helped reduce RSV-associated hospitalizations

by 84.2% compared to placebo, Merck ( MRK ) said.

The incidence of treatment-related side effects were

comparable between the clesrovimab and placebo groups, Merck ( MRK )

said, adding that there were no treatment or RSV-related deaths

during the study.

Merck ( MRK ) had said in July that the shot met the main goal in

the study, but did not give details.

If approved, clesrovimab will compete in the U.S. market

with Sanofi and AstraZeneca's ( AZN ) antibody therapy

Beyfortus.

The FDA approved Beyfortus last year to prevent RSV

infection in infants and toddlers, also administered once per

season.

In a separate late-stage study, Beyfortus showed a 74.5%

reduction in the incidence of lower respiratory tract infections

requiring medical care in infants.

Swedish Orphan Biovitrum's preventive RSV

therapy Synagis is also available as a monthly injection.

Merck ( MRK ) reported on Thursday that clesrovimab had a comparable

safety profile to Synagis, citing interim results from a

separate late-stage study.

Pfizer's ( PFE ) RSV vaccine, Abrysvo, is approved for use

in pregnant women to prevent RSV infections in babies during the

first six months after birth.

RSV, which typically causes cold-like symptoms, is a leading

cause of pneumonia and death in babies and older adults. The

virus leads to 177,000 hospitalizations and 14,000 deaths

annually in the United States.