Since HIV, the virus that causes AIDS, was discovered in 1982, scientists around the world have been trying to create a vaccine against it.

But 28 years later after its discovery, and 22 years after the first World AIDS Day on December 1, 1988, the world is still waiting for the big breakthrough.

Nevertheless, scientists haven't given up yet. They know that a well tolerated, effective vaccine could effectively stop the worldwide spread of AIDS.

Developing an AIDS vaccine is an ambitious undertaking. There have been signs of promise, but setbacks as well, largely due to the changing nature of the virus. The fact is, there is no single strain of the human immunodeficiency virus (HIV), but many viruses, all of them slightly different.

"The virus is constantly changing, altering its structure, its genetic composition. That makes it harder for the immune system to fight," said Gerd Faetkenheuer, a professor at the University Clinic in Cologne, in an interview with Deutsche Welle.

When a person is infected with HIV, his or her immune system develops antibodies that fight the virus, but he or she is unable to stop it from spreading.

Simulated antibodies created in the lab

"Everyone who is infected, every patient, has antibodies. But these antibodies don't protect against the virus - as a rule, they just indicate it," Faetkenheuer said.

Researchers have been able to create simulated antibodies in the lab that are better than natural ones. They can protect people from numerous HIV strains and can even stop the virus from entering and infecting cells. But it's not clear whether these molecules will be able to function outside of the lab.

A further approach to vaccine research aims to teach the immune system what HIV-infected cells look like, so that the body can recognize the cells and get rid of them. According to Faetkenheuer, this kind of vaccine wouldn't be able to prevent infection, but could at least teach the body how to control it.

"We need immune cells that can recognize and kill the virus," he said. "A major problem in HIV infection is that the virus attacks the immune cells as well. You can even say that it attacks the most important cells of the immune system - the helper cells. They control the immuno-response."

The Thai exception

None of the possible vaccines that have been tested on people so far have proved effective - with one exception.

In Thailand, a combined vaccine was effective to a certain level. Its double aim was to stimulate antibody production while teaching the immune system to recognize infected cells. In a test group, those vaccinated showed 31 percent fewer incidents of infection.

This is the first small success after a series of setbacks. Yet there is one major problem: to this day, researchers cannot explain how the vaccine worked, and they aren't sure whether or not the results can be trusted.

"[31 percent] is a very slight difference, which also can be affected by external factors," Faetkenheuer said. "So we can't be sure if it was a real result, or if external factors that we haven't yet identified played a role."

Looking for answers in healthy populations

Researchers hope that a new, detailed analysis of the Thai experiment - already underway - will bring an answer to this question. Results are expected in around two years.

So what does a vaccine need to be able to do in order to protect someone from contracting HIV?

Dr. Bruce Walker, an AIDS expert at Boston University, is looking for the answer. He is testing carriers of the HIV virus who have the unusual ability to control the virus to the point where it almost doesn't replicate at all.

Walker has discovered genetic material in these subjects that doesn't exist in other HIV patients.

"The challenge is now for us to reach the point that we understand the mechanism and find out how to really control the virus," he said.

But there is likely to be a long road before that point is reached. There may never be a 100 percent reliable vaccine against HIV - but even a vaccine with a 50 or 60 percent protective effect could help to slow the spread of the virus, experts say.

Multifaceted strategy for fighting the disease

A complete disease-fighting strategy wouldn't rely entirely on the vaccine. Other techniques include: condoms, male circumcision, and medication. Because as it turns out, HIV-infected patients who are medically treated are less infectious, Faetkenheuer said.

"At present, the most successful tool we have isn't vaccination, it is treatment," Faetkenheuer said. "When people are treated, it means that fewer people will be infected."

The problem with that, however, is that even in wealthy Europe, about half of the people who are HIV positive don't know it.

"If they don't do an AIDS test, they can infect other people without even wanting to," said Jens Lundgren, a professor at the University of Copenhagen. "They don't know that they are a risk for their partner, and a risk for society."

As ever, taking a simple AIDS test is one method for proving an existing infection - and for getting early treatment. And it is still the surest way to know whether or not you could spread the virus to other people.

Author: Martin Winkelheide/jen
Editor: Cyrus Farivar