WASHINGTON (Reuters) - A once-a-day pill combining two Gilead Sciences Inc AIDS drugs reduced the HIV infection rate by nearly 44 percent in high-risk gay and bisexual men, researchers reported on Tuesday.

Members of Thalassemia and AIDS prevention society, a non-government organisation, take part in a candlelight rally on the eve of World AIDS Day in the eastern Indian city of Kolkata November 30, 2008. REUTERS/Parth Sanyal

Men who took the pill the most consistently had more than a 70 percent lower risk over two years, the U.S. government study in Peru, Thailand, South Africa and elsewhere found.

It is the first study to show that taking drugs before infection can reduce the risk of HIV transmission and has the potential to be a weapon in the fight against the fatal and incurable virus, the researchers said.

It makes for a trifecta in AIDS prevention research, coming months after a study released in July showing a gel could help protect women against the virus and one last year showing a vaccine had a partially protective effect.

“These results represent a major advance in HIV prevention research,” Dr. Kevin Fenton of the U.S. Centers for Disease Control and Prevention said in a statement.

The international team of researchers studied 2,499 gay, bisexual and transgender men at high risk of infection with the AIDS virus. Half took Truvada, a pill containing Gilead’s drugs tenofovir and emtricitabine, and half got a dummy pill.

After about 2 1/2 years, 100 of the men became infected with the human immunodeficiency virus that causes AIDS -- 36 who took Truvada and 64 who received a placebo.

“This means that the daily use of Truvada reduced the risk of HIV acquisition by 43.8 percent,” Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, which funded the study, told reporters.

People often forget to take pills, so the researchers took regular blood tests. The men who had active drug in their blood 90 percent of the time had a 73 percent lower risk of infection than those taking placebo.

FOLLOWING DIRECTIONS

All those who were given Truvada and became infected had either very low levels of the drug in their blood or none at all.

“We think the best explanation for why the drug was not in the body is that the people were not taking it,” Dr. Robert Grant of the Gladstone Institutes and the University of California San Francisco, who led the study, said in a telephone interview.

Fauci said the study showed the drug was safe, caused only mild side effects and the men who took it did not develop resistance. This meant the drug stayed effective against the virus, with the exception of three cases who were already HIV-infected when they started taking the pills.

All 2,499 men will be offered “Prep”-- pre-exposure prevention -- with free Truvada pills. One thing the researchers want to find out is if the men will take the pills more consistently now that they know they work, are safe, and that they are getting the real drug and not a placebo.

Gilead supplied Truvada but was not otherwise involved in the study, paid for by NIAID and the Bill & Melinda Gates Foundation.

The drug costs $1,000 a month in the United States but Gilead lets several Indian companies make cheap generic versions costing as little as 40 cents a dose for use in Africa and other developing nations.

Dr. Howard Jaffe, president of the Gilead Foundation, said the company was not planning any price changes.

Fauci said some people were already getting Truvada “off label” from their doctors to prevent HIV from their doctors. But Jaffe said he was not sure if Gilead would ask the U.S. Food and Drug Administration for permission to market the drug for preventing HIV in addition to treating the infection.

“It’s a debate that really is bigger than Gilead,” Jaffe said in a telephone interview.

Activists called for immediate wider testing.

“Every year 2.7 million people are infected with HIV, and Prep has the potential to help bring those numbers down. We have a moral obligation and a public health imperative to quickly act on these results,” said Mitchell Warren, executive director of the HIV advocacy group AVAC.