US officials said 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 US Centres 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 yesterday.
The trial of 1200 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 behavioural and clinical safety and adherence,” the CDC said in a statement.
One problem is that new HIV infections are becoming less common in Botswana, where nearly a quarter of adults are infected.
“The drops in incidence that we are seeing in Botswana and elsewhere are welcome news, requiring new and innovative ways of designing, running and funding trials and of working with communities,” said Mitchell Warren, executive director of the group AVAC: Global Advocacy for HIV Prevention.
“The trial, however, will provide critical information on safety and adherence to help guide potential implementation planning should PrEP prove effective in other trials,” the CDC said.
Other, similar trials are under way in the United States, South Africa, Thailand, Brazil, Peru, Kenya, Uganda and elsewhere.
Researchers are also looking for other ways to prevent infection, including by circumcising men.
There is no vaccine against the AIDS virus yet although work continues to make one, and researchers are also working on testing microbicides gels or creams that could be used to help prevent sexual transmission of the virus.