According to a new study an experimental vaccine by Sanofi-Aventis may curb a virus called cytomegalovirus ( CMV) in women, which might reduce CMV-related birth defects in their children.

However the new vaccine is not expected to be available in the market in the near future as the drug maker said it's reworking the formulation to try to make it even more effective, which would necessitate further trials.

According to the CDC, CMV is the most common virus transmitted to a pregnant woman's fetus and doesn't typically show symptoms in adults. About one in 150 children is born with CMV infection, and about one in 750 U. S. children are born with or develop permanent disabilities including hearing problems because of CMV.

The vaccine was tested on 464 girls and women in the age group of 14 and 40, who were not pregnant and who had tested negative for signs of CMV infection between
1999 and 2007. Women were divided into two groups and one was given three shots of the vaccine while the other group got three shots of a placebo over a six month period and then tested for CMV infection.

In the group that received the CMV vaccine 8 % of the women developed CMV as compared to the placebo group where 14 % of the women developed the infection. That translated into a 50% reduction in the infection rate based on a clinical analysis, according to results published online Wednesday in The New England Journal of Medicine.

"Vaccine efficacy was 50%," said Robert Pass, MD, of the pediatrics department at the University of Alabama at Birmingham and lead author of the study.

The side effects noted were injection site reactions, chills, joint pain, and muscle pain which were more common in the vaccine group than in the placebo group though these were mild and temporary.

Out of the fifteen babies that were conceived three to 40 months after the last shots were given and had serious adverse effects, seven were born to women who received the vaccine.

The researchers said further studies were needed as CMV is a "large and complex virus" and that people who've had CMV infection can become infected by new CMV strains.

The CMV study was partly funded by Sanofi Pasteur, which makes the experimental CMV vaccine. While the study was underway Sanofi acquired the rights to the vaccine which was previously being developed by Chiron, a company later acquired by Novartis AG.

The vaccine included a Sanofi antigen - the ingredient that targets the virus - and a Chiron adjuvant, which is the component that can boost efficacy of the antigen. In order to gain regulatory approval a larger, multi-year trial would be needed to establish the vaccine's safety and efficacy.

However Sanofi doesn't plan to go to a late-stage trial with this formulation and is assessing different antigens and adjuvants "to enhance the breadth and potency of the immune response," said spokeswoman Susan Watkins. These would have to be tested in a new round of human studies, and Watkins said it's too early to predict regulatory filing dates or vaccine pricing.