A US biotechnology company has been giving details of a vaccine against Aids, which it hopes could be available by 2005, to delegates attending the International Aids Conference in Barcelona.

I think we will get protection [from the virus], but I don't know what level we'll get

Donald Francis, VaxGen

The head of VaxGen, Donald Francis, said the vaccine worked on chimpanzees and he was optimistic about the results of trials on humans, due to be published next year.

VaxGen's vaccine will be part of the biggest-ever HIV vaccine trial due to begin later this year in Thailand with the involvement of 16,000 people.

Reports of scientific progress were accompanied by warnings that rich nations needed to spend more to help bring the epidemic under control.

Malaysian activist Irene Fernandez told the conference that North American and European countries were not meeting their targets for foreign aid set by the Organisation for Economic Co-operation and Development (OECD).

If they did, she said, there would be enough money to fund Aids-prevention programmes.

The six-day conference is organised by the United Nations agency UNAids and is being attended by 15,000 delegates.

	:	Aids pandemic
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Licence conditions

In the Thai trial, VaxGen's product will be tested in combination with another vaccine, designed to produce a different type of immune response. Scientists hope this will result in a higher level of protection than either vaccine would induce on its own.

Potential vaccine

Prevents infection by stimulating the production of antibodies Being tested on high risk groups If all goes to plan, could be licensed within five years Q&A: Aids vaccine

But VaxGen is optimistic that its product will also work as a sole vaccine.

"I think we will get protection [from the virus], but I don't know what level we'll get," Mr Francis said.

"If all goes well, [the vaccine] could be available by the end of 2004 or early 2005."

Campaigners have given a cautious welcome to VaxGen's announcement, but say it is necessary to wait for the analysis of clinical trials.

BBC health correspondent Chris Hogg says that 21 years after the fight against Aids began, only eight vaccines are currently being tested on humans to any significant degree.

Most of these are still in the early stages. VaxGen is the only company testing its products on humans in an end-stage trial.

To be granted a licence, however, it will have to show the vaccine is effective in at least one-third of patients.

Immunisation hopes

Jose Esparza, co-ordinator of the UNAids HIV vaccine initiative in Geneva, said VaxGen's announcement was "premature", although he praised the company's commitment to developing a vaccine.

We would hope to use it as part of immunisation for every child so we can put an end to this terrible disease

Dr Seth Berkley, IAVI

"If the vaccine is effective then we will have a cause for celebration, but even then it will not be the end of the epidemic," he said.

The umbrella body promoting research, the International Aids Vaccine Initiative (IAVI), warned that preparations needed to begin now for the distribution of a successful vaccine to the countries most in need.

Most importantly, it eould have to be made affordable.

IAVI president Dr Seth Berkley told the BBC that vaccination would initially be targeted at high-risk groups such as intravenous drug users and commercial sex workers.

But he said it was hoped one day that a vaccine would be available for everyone.

"We would hope to use it as part of immunisation for every child so we can put an end to this terrible disease."

Blocking out HIV

The conference also heard about a drug which tests have shown cuts the levels of HIV in patients by stopping it entering blood cells.

The injectable T-20 drug, made by Roche Holding AG of Switzerland and US biotech firm Trimeris Inc is due to go on to the market early next year.

It is said to offer hope to patients with serious drug resistance problems.

Existing treatments attack HIV only after it has entered cells.

A study presented to the conference showed three quarters of gay and bisexual men in US cities who were infected with HIV did not know they had the virus.