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 long-term 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 still 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 be needed so that people
continue to practice safe behaviors.
Preventive versus Therapeutic HIV Vaccines
Preventive HIV vaccines are designed to protect HIV-negative people and to control the spread of HIV. They are not designed to cure AIDS.
Multiple HIV vaccines may be necessary to prevent infection
or disease in the same way multiple drugs are needed to treat
people already infected with HIV.
Researchers are also evaluating
therapeutic vaccines to treat people
with HIV infection or AIDS. While the same vaccine may be
tested for both preventive and therapeutic effects, what works to
prevent HIV infection may not necessarily work to treat people
who are already infected with HIV.
Phases of Testing HIV Vaccines
Vaccine development requires several years of research in
laboratories and animals before testing in humans can begin.
A potential vaccine goes through three phases of testing in
humans before the Food and Drug Administration (FDA)
can consider licensing it for public use. The three phases of
preventive HIV vaccine clinical trials are:
- Phase I - involves a small number of healthy volunteers
(HIV-negative) to test the safety and various doses of the
vaccine; usually lasts 12 to 18 months.
- Phase II - involves hundreds of volunteers (HIV-negative)
to test the safety and immune responses of the vaccine; can last
2 to 4 years. The Step Study is Phase II trial.
- Phase III - involves thousands of volunteers (HIV-negative)
to test the safety and effectiveness of the vaccine; can last 3 to
4 years.
Throughout all phases of human testing, independent reviewers
regularly monitor the study to ensure the safety of the volunteers.
