An experimental vaccine may curb cytomegalovirus ( CMV) in women, which might reduce CMV-related birth defects in their children.That’s according to a new study, published in The New England Journal of Medicine.

CMV is common and it doesn't typically show symptoms in adults. It can pass from mother to fetus, making birth defects -- including hearing problems -- more likely.

According to the CDC, CMV is the most common virus transmitted to a pregnant woman's fetus. About one in 150 children is born with CMV infection, and about one in 750 U.S. children is born with or develops permanent disabilities because of CMV.

CMV Vaccine Study

The new CMV vaccine study included 464 women 14-40 in Alabama. When the study started, none of the women were pregnant and none had a history of CMV.

The researchers gave the women three shots of the experimental CMV vaccine or a placebo.

During the next three years, 8% of the women who had gotten the CMV vaccine developed CMV infection, compared to 14% of women who had gotten the placebo shots.

"Vaccine efficacy was 50%," write the researchers, who included Robert Pass, MD, of the pediatrics department at the University of Alabama at Birmingham.

Injection site reactions, chills, joint pain, and muscle pain were more common in the vaccine group than in the placebo group.

Most adverse events were mild and temporary. But one woman in the vaccine group had a fever, rash, muscle pain, and weakness that left her unable to walk after the second dose of the vaccine; she recovered over the next six to seven months. Another woman who had gotten the placebo shots had numbness in her feet and hands 10 weeks after the second dose; her symptoms improved with time. It's not clear what caused those symptoms.

Fifteen babies, who were conceived three to 40 months after the last shots were given, had serious adverse events. Seven of those babies were born to women who had gotten the experimental vaccine.

Further studies are needed, the researchers note. They point out that CMV is a "large and complex virus" and that people who've had CMV infection can become infected by new CMV strains.

"The development of a CMV vaccine remains a daunting task," states an editorial published with the study. "Even so, the prevention of the burden of congenital CMV infection -- despite all the challenges -- must remain a high priority," write editorialists Cornelia Dekker, MD, and Ann Arvin, MD, of Stanford University School of Medicine.