The usefulness of HIV/Aids clinical trials should be assessed to ensure scientific gains are balanced with a concern for human life, Health Minister Manto Tshabalala-Msimang said on Thursday.

"There is a need for us to ... look at the total picture whether we are making any progress in finding new tools to respond to HIV infections without putting more lives at risk," she said.

The minister was speaking at a colloquium on HIV/Aids vaccines and microbicide research in Boksburg.

"Is it not perhaps time to pause and redirect the energy and resources to finding some important basics in our scientific query?"

Tshabalala-Msimang also said the government had a responsibility to protect the "vulnerable members" of society used in the trials.

"The poor and historically disadvantaged communities provide an invaluable platform for scientists to conduct research in HIV and Aids," she said.

"The democratically elected government has a responsibility to ensure that planned research is necessary; that it is conducted in an ethical manner."

Most importantly, she said, was that the research did not expose the participants to unnecessary risks.

At the end of her address, Tshabalala-Msimang thanked participants for "not having placards saying I should be fired...

"...Because I think we must get to the bottom of this (Aids pandemic) which the president [Thabo Mbeki] in 2002 described as a catastrophe".

Speaking after the colloquium, National Institute of Communicable Diseases' Aids Virus Research Unit professor Lynn Morris said scientists did not know everything about the basic science behind building a successful HIV/Aids vaccine.

"That's why we need to keep going. We need to try harder because giving up is definitely not an option," she said.

Morris said it took decades to make vaccines and often there was pressure to stop trials when research appeared to reach unsuccessful outcomes.

"Scientific challenges" were currently the most significant limiting factor in HIV vaccine development.

"Its a tough nut to crack," Morris said.

She added some recent disappointing results from trials meant researchers were at a crossroads."We are rethinking things".

She said in recent trials the product might not have worked but the trial was a success.

"It may not be the result we hoped for but questions were answered.

"There is still optimism in the field but we probably need to expect more failure than success..

"A vaccine is not around the corner and even if we do have one it's not going to be a magic bullet. Other interventions will also be needed.

"We need to do more basic research and continue to conduct human clinical trials," she said.

Director of the Perinatal HIV Research Unit Professor Glenda Gray also backed human clinical trials.

"Research in humans is essential to moving forward to an Aids vaccine."

She said researchers felt there was a need to stop "doom and gloom "statements that border on the ridiculous" about the outcome of recent trials.

At the moment it was "not business as usual," she said.

Researchers were re-assessing the way forward.

Yet while there were no products ready for large-scale trials,smaller trials should continue she said.

Medical Research Council professor Gita Ramjee said every trial brought new knowledge.

"We learn every time and we try new things. "If we knew what to expect we wouldn't be doing research," she said. The risks faced by participants were a key consideration, Morris added.

"These (clinical trials) are run under high scrutiny and monitored at every level, and safety is undeniably the first priority."

Wits University Reproductive Health and Aids Unit professor Helen Rees said there was a need to ensure the trials were scientifically sound in order to protect the participants.

She added there were "all sorts of checks and balances for all clinical trials".

Participants went through a process of giving informed consent and an ethics committee checked this, said Rees.- Sapa