Infants who received a single dose of the inexpensive antiviral drug nevirapine (NVP) soon after birth - and whose mothers took one dose of the same drug during labor - were 41 percent less likely to acquire HIV at birth or during breastfeeding than infants in infant/mother pairs who were treated with a multi-dose regimen using AZT, according to new results from a study funded by the National Institute of Allergy and Infectious Diseases (NIAID), one of the National Institutes of Health.

In a long-term study that began in November 1997, Ugandan and U.S. researchers have found that the initial advantage gained by infants who, along with their mothers, received one dose of NVP was largely sustained by the group of children until they reached 18 months of age, with few serious side effects attributable to NVP. This finding offers compelling new evidence that short-course NVP effectively and safely reduces the number of children who eventually become infected with HIV.

"This landmark study could have far-reaching implications in resource-poor countries where breastfeeding and mother-to-child HIV transmission are both common," says Anthony S. Fauci, director of NIAID. "Indeed, the potential for lessening the burden of HIV/AIDS with this NVP regimen makes this work a very important public health breakthrough."

This study, named HIVNET 012, has tracked the efficacy over time of a single dose of NVP to a mother and her infant in comparison with a more complicated AZT treatment in preventing HIV transmission. HIV can be transferred to an infant before birth, during birth or through the mother's breast milk. More than 600 HIV-infected pregnant women were enrolled in the study. One group of women received a single dose of NVP during labor, while their infants received one dose within three days of birth. A second group of women received AZT one or more times during labor, while their infants received doses twice daily throughout the first week. This regimen was followed because of AZT's shorter half-life. A third, much smaller group of women and their infants received a placebo. (The placebo was discontinued early in the study when there was evidence that AZT was superior to the placebo.) Approximately 99 percent of the study participants breastfed their children. After 18 months, most of the women had completed breastfeeding, with the average duration lasting 9 months.

The researchers speculate that the long-lasting benefits of NVP are not due to any persistently protective role provided by the drug itself since it is metabolized within 10 days; rather, infants receiving NVP, as with some other effective antiretroviral regimens, gain a protective advantage during the first few weeks of life, the time of greatest risk of HIV transmission. Although babies in both groups continued to acquire HIV throughout the study, they did so at approximately the same rate, enabling the NVP group to maintain its overall reduced risk even as the children grew older.