Scientists looking for a vaccine against the Aids virus can be forgiven for wondering at times whether they made the right career decision.

For more than a quarter-century, their quest has been littered with setbacks while colleagues who work on HIV treatment have been showered with success.

Promising avenues have led to dead ends and long, costly trials of prototypes have ended in failure, saddling the vaccine field with a reputation for lucklessness.

But two pieces of good news have suddenly boosted morale.

Even though a vaccine still lies over the horizon, at least a path has now emerged for getting there, say experts interviewed at the Aids Vaccine 2009 conference, ending in Paris on Thursday.

On 3 September researchers in the United States discovered two potent antibodies — the frontline troops in the immune system — that expose what may prove to be a viral Achilles' heel.

On 24 September US and Thai researchers unveiled the results of the biggest vaccine trial ever.

'Too weak'

Tested among more than 16 000 Thais, shots of ALVAC and AIDSVAX vaccines offered 31.2-percent protection against the risk of infection by the human immunodeficiency virus (HIV).

This is far too weak to make it a vaccine for public use.

And nagging questions arise: why does the vaccine's effect seem to wane over time? Why does it seem to be less effective among people who are most at risk from HIV infection? And could it work in Africa, epicentre of a pandemic that has claimed 25 million lives and left some 33 million others infected?

Even so, the trial is scientific gold.

It proved at last that the immune system can be taught to recognise and devise a shield, even partially, against a notorious shape-shifting foe.

"We now have a proof of concept. It's the first time we've been able to show that," said Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases (NIAID).

"ALVAC/AIDSVAX is not in itself the answer. It's a start on the road to a vaccine, whereas, before, we didn't even know where the road was."

"The Thai tests have provided a vital pick-me-up," agreed Jean-Francois Delfraissy, director of France's National Agency for AIDS Research (ANRS).

AFP

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