Regeneron Pharmaceuticals is pulling the plug on an experimental therapy in development for preventing respiratory syncytial virus (RSV) infection in infants, after a disappointing performance in a late-stage trial.

The firm said that a Phase III study assessing suptavumab, an antibody to RSV, failed to meet its primary endpoint of preventing medically-attended RSV infections in infants.

The drug did show signs of efficacy in a subgroup of patients, and adverse events were generally balanced between the treatment arm and a placebo.

However, Regeneron said it plans to discontinue further clinical development of the antibody.

"We are disappointed in these results, as we had hoped suptavumab might offer a new option for the thousands of infants impacted by serious RSV infections every year," said George Yancopoulos, president and chief scientific officer of the group.

Full data from the trial, which enrolled 1,149 healthy pre-term infants, is to be presented at a future medical congress.