Oct 22 (Reuters) - Moderna ( MRNA ) said on Wednesday it

would discontinue development of its experimental vaccine to

prevent cytomegalovirus, a common cause of birth defects, after

it failed to meet the main goal of a late-stage trial.

Shares of the drugmaker were down over 4% in extended

trading.

The study tested the vaccine, mRNA-1647, in about 7,500

women aged 16 to 40. It showed efficacy ranging between 6% and

23%, which was below Moderna's ( MRNA ) target.

"We are clearly disappointed by the failure to prevent

primary infection because it means there is still no vaccine for

the prevention of congenital CMV despite the many decades of

work by the field," said Stephen Hoge, MD, president of Moderna ( MRNA ).