By Martin Hutchinson
After two decades of research into an HIV vaccine, there comes a bleak message from one of those leading the hunt.
Professor David Baltimore, president of the American Association for the Advancement of Science, said that while efforts are continuing, there is "little hope" of success.
"In 1984, we were told that as the virus had been found, a vaccine should be just around the corner," he said.
"But we are no closer to a vaccine now than we were then."
This plunge in scientific morale follows the collapse, last year, of a massive vaccine experimental vaccine project.
It quickly became obvious that, despite 10 years of hard work, and millions of dollars spent, the jab offered zero protection in the real world.
Elsewhere, however, the mood is far less downbeat.
Professor Quentin Sattentau, working on a vaccine at Oxford University, said that while realism was important, a breakthrough could still come quickly.
"Of course, it's possible that we will never find a vaccine for HIV. But that doesn't mean that we should stop looking.
"We are making small steps all the time, and we can never predict what science will discover at any moment."
HIV is quite unlike other viruses which have fallen to the vaccine-makers over the past two centuries.
It has a remarkable ability to disguise itself against the body's defences, constantly changing to avoid detection.
This means that vaccines which rely on using a recognisable part of the virus to prime the immune system can be ineffective almost as fast as they enter the body.
"This variability is the biggest problem - it's much faster, for example, than influenza," said Professor Sattentau.
Another problem is its lethal nature. Normally science can learn from the survivors of a viral infection, but in HIV, although some live with the virus for decades, there are no reliable reports of anyone managing to clear it from their bodies entirely.
To focus entirely on vaccine would ignore the massive strides made in HIV treatments - the latest crop of antiretroviral drugs offer the prospect of almost normal lifespan for some patients.
However, as research published only this week showed, they cannot fully purge the virus from the body.
Despite the remaining glimmers of hope from other vaccine projects, some HIV experts have welcomed Professor Baltimore's comments.
Deborah Jack, the chief executive of the National Aids Trust, which lobbies governments for more research funding into HIV vaccines, said that there was no reason to give up hope.
"What we have to remember is that it took 47 years to produce a polio vaccine, and 42 years to make one for chickenpox.
"There are currently 30 trials into vaccines running at the moment around the world, and even if they fail, we will learn more about HIV from them."
And Lisa Power, from the Terrence Higgins Trust, said that hype from pharmaceutical companies and other about the prospects for a vaccines risked drawing attention away from the only practical methods available today to those at risk of infection.
"I would commend him on his comments," she said. "We need to balance the hopes for the future with what we can do now.
"Many people would welcome an injection which would allow them to have unprotected sex for the rest of their lives, but unfortunately it's not happening in the real world.
"Safe sex, testing and treatment - these are the ways to prevent its spread," she said.
"The good news is that HIV is starting to lose - but it's going to be trench warfare, taking ground patient by patient."