What is an HIV vaccine?

A preventive HIV vaccine is a substance that teaches the body's immune system to recognize and protect itself against HIV - the virus that causes AIDS. All of the HIV vaccines currently being tested for humans are made from man-made materials that cannot cause HIV infection.

Scientists believe that an effective HIV vaccine, given before exposure to HIV, could have a number of possible outcomes. These include:

• Preventing infection in most people
• Preventing infection in some people
• Preparing a person's immune system to block continued infection and eliminate the virus (Vaccines against measles, mumps and polio work this way.)
• Delaying or preventing the onset of illness or AIDS

The goal is to develop a vaccine that is 100 percent effective and protects everyone from infection. However, even if a vaccine only protects some people, it could have a major impact on controlling the epidemic. A partially effective vaccine could decrease the number of people who get infected with HIV. Those people, in turn, would not pass the virus on to others. Even when an HIV vaccine is developed, education and other prevention efforts will still be needed so that people continue to practice safe behaviors.