Health Report.South African researchers at the international AIDS conference in Vienna, Austria have announced major progress in the fight against the disease. The researchers say their study showsa vaginal gel substance reduced the risk of HIV infection among women who used it.The gel contains tenofovir.This is a common anti-retroviral drug used to treat people with HIV, the virus that causes AIDS.The study was done by South African scientists with the Center for the AIDS Program of Research in South Africa.It involved almost nine hundred sexually active women between the ages of eighteen and forty.All were from KwaZulu-Natal, South Africa. Half were given the gel containing tenofovir. The other half were given a gel without an active substance. They were told to use the gels twelve hours before sexual intercourse and again within twelve hours after sex.Both groups were told the gels were experimental. They were advised to use another form of HIV prevention.The study lasted thirty months. Women who used the tenofovir gel reduced their risk of HIV infection by thirty-nine percent. And the study found that the women who used the gel more often had even better results. Women who used the gel more than eighty percent of the times when they had sex had fifty-four percent fewer HIV infections.The scientists say the tenofovir gel was also effective against another sexually spread disease. The gel reduced the rate of infection of herpes simplex-two by fifty-one percent.Health experts say the results of the study show that tenofovir gel can empower women. They say it will enable them to protect themselves from HIV infection when involved with sexual partners who refuse to wear condoms.However, researchers say they will study why the geldid not protect in all cases. Some scientists say the amount of tenofovir in the gel may be too low. Others say some women may have had sex with infected men who had very high amounts of the virus. Still others said some women may have had vaginal conditions that made them more likely to become infected. The researchers also say they will carry out more studies to confirm the results.And that's the VOA Special EnglishHealth Report written by Caty Weaver. Transcripts, MP3s and archives of our reports are at 51voa.com.