A protective gel made using the HIV drug tenofovir reduced HIV infections in women by 39 percent over two and a half years - the first time such an approach has protected against the AIDS virus, South African researchers reported.

The results show it may be possible to slow the spread of the disease by giving women a way to protect themselves, Dr. Salim Abdool Karim at the University of KwaZulu-Natal in Durban, South Africa said in results to be released on Tuesday at the International AIDS Conference in Vienna.

Researchers have been trying for years to formulate a microbicide - a gel, cream, ring or tablet inserted into the vagina or rectum before sex to prevent transmission of the human immunodeficiency virus that causes AIDS. But past efforts have had disappointing results.

“Boy, have we been doing the happy dance,” Karim told Reuters in a telephone interview.

In addition, the gel reduced the risk a woman would get genital herpes by 51 percent, a surprise finding that adds further benefits.

The trial of 889 women in the coastal city of Durban and a remote rural village in South Africa showed women largely used the gel as directed, Karim said, answering an important question about whether such a product could work in the real world.

Dr. Anthony Fauci of the U.S. National Institute of Allergy and Infectious Diseases said he believed it would be possible to design studies that will get even better results.

“I have a pretty firm conviction that we are going to do better than this,” Fauci said in a telephone interview. “Microbicides are going to get on the map.”

SLOWING A PANDEMIC

In this test of a microbicide, called Caprisa, researchers used for the first time a prescription HIV drug in the mix, Gilead Science Inc’s tenofovir. Studies in monkeys have strongly suggested it can protect against both vaginal and rectal infection.

In Africa, where most of the world’s 33 million HIV cases are, most new cases are in young women infected by older men. Young boys aged 15-19 do not have high rates of HIV, but girls this age already do.

The Caprisa trial was a classic medical clinical study, with half the women using the gel before and after sex, and half being given a placebo. No one knew who got the real drug.

The women kept track of the applicators, which resemble applicators used to insert tampons, and gave them to researchers so they could be sure when the gel was actually used.

All the women were also given condoms and counseling about sexually transmitted diseases and they were tested for HIV once a month.

After 30 months, 98 women became infected with HIV - 38 in the group that got tenofovir in the gel and 60 in the group that got placebos. “We showed a 39 percent lower incidence of HIV in the tenofovir group,” Karim said.

When they checked the data, it turned out that tenofovir lowered the risk of infection by 50 percent at 12 months but then the efficacy declined. Women who used the gel more consistently were much less likely to be infected.

“Why is our effectiveness going down over time? Essentially it is a matter of adherence,” Karim said. “We are telling these women we have no idea if this works and we are also telling them we don’t know it is safe.”

Once women understand the gel will protect them, safely and without side-effects, Karim said, he believes they will use it more consistently.

“It needs to be marketed and packaged,” Karim added. “We had it in a boring white package. We need to make this a sexy gel.”

The study was funded by the South African government and USAID. Gilead supplied the drug for no charge but was not otherwise involved.

Karim does not know how much each dose would cost but said the applicators and gel cost just pennies.

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By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters)