A major trial into a possible vaccine for HIV has ended in disappointment for researchers.
The quest for an HIV vaccine continues
Preliminary results from the AIDSVAX trial in Thailand show it does not work, say its makers VaxGen.
Those given the vaccine were no less likely to contract HIV, and the jab did not slow the progress of the disease.
VaxGen president Donald Francis said the failure called on the research community to "redouble" efforts to find a successful vaccine.
While earlier trials had not offered compelling evidence that AidsVax was likely to succeed, in Thailand it had reached the "final stage" of testing, in which large numbers of people were given the jab to see how well it performed in wider society.
However, the announcement from VaxGen this week confirms earlier signals from the test area that success was unlikely.
While there were no major side-effects, there was no difference between vaccinated and unvaccinated people when it came to vulnerability to HIV.
In all, more than 2,500 injecting drug users in Bangkok were involved in the test, with half given the actual vaccine and half a "placebo" with no ingredients.
During the trial, 105 volunteers given the placebo caught HIV, compared with 106 vaccinated volunteers.
The rigorous make-up of the trial mean that the results are likely to be reliable, and the attention of researchers is now likely to turn towards other Aids vaccine projects currently underway in Africa and elsewhere.
A number of potential jabs are at an advanced stage of testing, although final results will not be available for some time.
Donald Francis said: "The outcome of this trial is one more reminder of how difficult it is to combat HIV and how important it is for the internationl public health community to redouble the effort to develop an effective vaccine.
"Although we are disappointed with the outcome, VaxGen and our Thai collaborators have created a model that can be used around the world for advanced clinical research of an HIV vaccine."
Results released in February this year revealed that a 5,000 person test showed no advantage in white people - but some prospect of success in black or Asian populations.
The Thai results are a blow to those encouraged by February's results.
The vaccine does not actually contain any genetic material from the virus itself, but just synthetic versions of proteins found in the virus.
The idea was that the immune system would become sensitised to these proteins, and launch attacks on any virus which contained them.