Last updated: 20 october, 2009 - 13:23 GMT
HIV vaccine: doubts over trial
Just a few weeks ago, some scientists thought they were one step closer to finding a vaccine for HIV/Aids.
In the large-scale trial in Thailand, a combination of vaccines seemed to give volunteers a protective effect of 31%.
However, new data, being published at a conference in Paris, is believed to question that assertion.
The BBC's Matt McGrath reports from Paris.
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First broadcast 20 October 2009
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