Although many man hours as well as millions of dollars have been devoted to finding an elusive AIDS vaccine, scientists now admit it may never happen.
In the poll, conducted by the Independent, many boffins believe that a vaccine against HIV is further away than ever.
A mood of deep pessimism has spread among the international community of AIDS scientists after the failure of a trial of a promising vaccine at the end of last year.
It was the latest in a series of setbacks in the 25-year struggle to develop an HIV vaccine.
The Independent's survey of more than 35 leading Aids scientists in Britain and the United States found that just two were now more optimistic about the prospects for an HIV vaccine than they were a year ago; only four said they were more optimistic now than they were five years ago.
Nearly two thirds believed that an HIV vaccine will not be developed within the next 10 years and some of them said that it may take at least 20 more years of research before a vaccine can be used to protect people either from infection or the onset of Aids.
A substantial minority of the scientists admitted that an HIV vaccine may never be developed, and even those who believe that one could appear within the next 10 years added caveats saying that such a vaccine would be unlikely to work as a truly effective prophylactic against infection by the virus.
One of the major conclusions to emerge from the failed clinical trial of the most promising prototype vaccine, manufactured by the drug company Merck, was that an important animal model used for more than a decade, testing HIV vaccines on monkeys before they are used on humans, does not in fact work.
This has meant that prototype HIV vaccines which appear to work well when tested on monkeys infected with an artificial virus do not work when tested on human volunteers at risk of HIV - a finding that will be exploited by anti-vivisectionist campaigners opposed to vaccine experiments on primates.
Anthony Fauci, the director of the US National Institute of Allergy and Infectious Diseases (NIAID), near Washington, told The Independent that the animal model - which uses genetically engineered simian and human immunodeficiency viruses in a combination, known as SHIV - failed to predict what will happen when a prototype vaccine is moved from laboratory monkeys to people.
"We've learnt a few important things [from the clinical trial]. We've learnt that one of the animal models, the SHIV model, really doesn't predict very well at all. At least we now know that you can get a situation where it looks like you are protecting against SHIV and you're not protecting at all in the human model - that's important," The Independent quoted him, as saying.