20091218

WASHINGTON (Reuters) - U.S. officials said on Thursday they will change directions on one trial in Botswana trying to show whether it is possible to prevent HIV infections by taking a daily pill because too few people are being infected.

There are also problems keeping people enrolled in the trial, so it will be adjusted to show instead how well people can stick to the routine, the team at the U.S. Centers for Disease Control and Prevention said.

"We are not giving up on the trial -- we are going to complete the trial. We just will not get all of the answers we set out to get," the CDC's Terry Butler said in a telephone interview.

The trial of 1,200 people was trying to see if people could prevent infection with the AIDS virus if they took a daily pill that combined two HIV drugs. It was using Gilead Sciences Inc's Truvada, a combination of two drugs called tenofovir and emtricitabine.

The CDC did not release the data on how many people in the trial became infected, and said there appeared to be no safety concerns with the treatment so far.

The study, called TDF2, is one of several globally looking at the new approach, called pre-exposure prophylaxis or PrEP. The idea is that a daily low dose of the drugs, which interfere with the ability of the virus to replicate, could also lower the risk of infection.

It has worked in monkeys and researchers are keen to see if it could provide an easy and cheap way to protect people from the virus, which infects 33 million globally and has killed 25 million people.

"The trial protocol and timeline will be revised to focus instead on the other remaining study questions -- primarily behavioral and clinical safety and adherence," the CDC said in a statement.