Live vaccines are artificially weakened versions of the organisms against which they protect. Live AIDS vaccines cannot be tested in man because of fears the weakened strain could revert to normal and cause disease. This factsheet outlines the useful information that has been gathered from primate studies of live vaccines.
IAVI. Understanding Live-Attenuated Vaccines - June 2008. What Can AIDS Vaccine Researchers Learn From Live-Attenuated SIV Vaccines? (2008)