October 17 2008 12:00 AM EST
November 17 2015 6:13 AM EST
It's easy to envision the moment of HIV infection as swarms of virus overpowering and hijacking your body's immune system. But the truth is more likely that only one tiny virus broke through your defenses, scientists report in the Proceedings of the National Academy of Sciences. Their genetic analysis of blood samples from 102 HIVers has shown that 76% of the cases could be tracked to a single virus infecting a single cell. And the remaining 24% were linked to infection by no more than five viral copies. While a grim reminder of just how efficient HIV is at establishing a foothold in the body, the researchers say, the study's findings also give hope to vaccine and microbicide researchers whose products need only prevent the transmission of a very small number of viruses.