But Gallo's discovery did not result in a vaccine to keep people from getting AIDS, as some at the time optimistically predicted. And without a vaccine, the AIDS virus has spread explosively in some of the poorest parts of the world, especially Africa, home to two-thirds of the more than 36 million people now infected. The possibility of an AIDS vaccine is just one of many unknowns as this epidemic enters its third decade. Breakthroughs cannot be predicted, nor can setbacks. Over the years, scientists have often questioned whether such a thing could ever be done.
Standard vaccines prompt the body to make antibodies that block infection.
Unfortunately, humans seem unable to manufacture antibodies powerful enough to stop the AIDS virus. Without them, a vaccine seemed unlikely. Now researchers are sounding more upbeat. In monkey tests, at least, several experimental vaccines seem to work well. While they may not prevent infection, they ward off AIDS by activating protective white blood cells called killer cells.