March 18 (HealthDay News) -- Women who were given an experimental vaccine for a viral infection that can cause serious problems in babies, known as cytomegalovirus, reduced their risk of infection by 50 percent for as long as three and half years after vaccination, according to new research.
"In many ways, this was a surprising result," said the lead author of the study, Dr. Robert Pass, a professor of pediatrics at the University of Alabama at Birmingham. "Many people in the field felt it would be very difficult to prevent infection in mothers. We thought the best we could hope for was a vaccine for women that would prevent infection in a baby."
Results of the study are published in the March 19 issue of the New England Journal of Medicine.
Cytomegalovirus, or CMV, causes severe hearing, mental or movement impairments each year in about 8,000 infants who develop the infection while still in the womb, according to the National Institute of Allergy and Infectious Diseases.
The virus is very common and spreads easily, according to Pass. He said one reason researchers thought an effective vaccine would be so difficult to develop was that the virus adapts to attacks from the human immune system. And unlike infection from such viruses as chickenpox and measles, people can be re-infected with CMV many years after an initial infection.
Anyone can develop a CMV infection, and healthy adults and children usually don't show symptoms of the infection.
The new vaccine is made from a single CMV protein that was combined with an experimental adjuvant, a substance that's added to vaccines to boost their efficacy.
The study was a phase 2 trial that included 464 women, all younger than 40 who had given birth in the past year and had not been infected with CMV. Half were given the vaccine, and the other half were injected with a placebo. Three doses were given: at the start of the study, a month later, and again at six months.
In the first year, 49 infections with CMV occurred, the study reported. In the placebo group, 31 women were infected with CMV, compared with 18 who had been given the vaccine.
Using a statistical model, the researchers estimated that women given the vaccine would be half as likely to develop a CMV infection over a 42-month period as those given a placebo.
Dr. Navid Mootabar, director of gynecology surgery and associate chief of obstetrics and gynecology at Northern Westchester Hospital in Mt. Kisco, N.Y., described the study as "very promising."
"If we can reduce the risk of a pregnant woman acquiring CMV, then we will reduce the many neurologic and congenital risks than CMV poses to a growing fetus," he said. "However, further larger studies will be needed to ensure the safety and efficacy of the vaccine before we should recommend it to all women."
Most of the funding for the study came from the U.S. National Institutes of Health, Pass said. Sanofi Pasteur, which makes the vaccine, also helped fund the study and provided the vaccine.
Pass said that he was not aware of specific plans to conduct a phase 3 trial. But he said that, given the results, he expects the pharmaceutical company to move forward with development of the vaccine.
SOURCES: Robert Pass, M.D., professor of pediatrics, University of Alabama at Birmingham School of Medicine and Children's Hospital of Alabama; Navid Mootabar, M.D., director, gynecology surgery, and associate chief, obstetrics and gynecology, Northern Westchester Hospital, Mt. Kisco, N.Y.; March 19, 2009, New England Journal of Medicine