(USA TODAY) -- Thirty years into the quest to develop a vaccine against the AIDS virus, scientists say they have greater understanding of the job ahead, as well as greater respect than ever for their adversary.

Researchers don't expect to have an effective vaccine for years, says Anthony Fauci, director of the National Institutes of Allergy and Infectious Diseases.

Yet recent discoveries of a series of "Achilles' heels" on the virus' surface have reinvigorated researchers' hopes of creating what could be the most powerful of all weapons to prevent and control the disease, says Bart Haynes, director of the Duke University School of Medicine's Human Vaccine Institute.

"We know the face of the enemy now," said Haynes, who presented his research Wednesday at AIDS 2012, an international conference in Washington. "We have some real clues about how to approach the problem."

Progress toward a vaccine has been slow, Haynes says, because the AIDS virus is unlike any adversary that scientists have ever faced. Among the key challenges:

Unlike the viruses that cause polio or smallpox, HIV is a retrovirus, Hayne says. So HIV doesn't just infect the body; it actually inserts itself into a cell's genome, or collection of genes, he says.

"An HIV vaccine must totally prevent infection," Haynes says. "Once infection occurs, the virus inserts into the genome, and the immune system can't kill it."

HIV is constantly mutating. Although the body tries to defend itself, it can't keep up with HIV's frantic pace, Haynes says. The body's struggle to create antibodies against HIV becomes a losing arms race, with HIV able to stay ahead of any weapon the body can muster against it, he says.

An effective vaccine, Haynes says, would stimulate the body to produce "broadly neutralizing antibodies" to fight HIV no matter how it mutates.

Scientists in the past couple of years have discovered several potential weak spots on the AIDS virus, which don't appear to change, even when the virus mutates, Haynes says. Researchers hope to create new vaccines to target these parts.

HIV has found ways to cloak itself, confusing the immune system.

So one major risk is that people who are vaccinated would make the proper antibodies, but their immune systems wouldn't recognize them. That could lead their immune system to flag the antibodies for elimination, says Wayne Koff, chief scientific officer at the International AIDS Vaccine Initiative.

Copyright 2012 USA TODAY, a division of Gannett Co. Inc.