What immune response should a vaccine elicit to prevent HIV infection? Two studies published online bring scientists closer to answering this question by identifying previously unrecognized attributes of antibodies that appear to have reduced the risk of HIV infection in the only clinical trial to show efficacy, albeit modest, of an experimental vaccine regimen in people.Earlier analyses of the results of that trial, known as RV144, suggested that antibodies to sites within a part of the HIV envelope called V1V2 correlated with reduced risk of HIV infection.

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