What Are Vaccines and What Do They Do?
A vaccine—also called a “shot” or “immunization”—is a substance that teaches your body's immune system to recognize and defend against harmful viruses (such as HIV) or bacteria before you get infected. These are called “preventive vaccines,” and you get them while you are healthy. This allows your body to set up defenses against those dangers ahead of time. That way, you won't get sick if you're exposed to them later. Preventive vaccines are widely used to prevent diseases like the flu, chicken pox, measles, mumps, rubella, polio, and hepatitis A and B.
There also is a relatively new type of vaccine, called a “therapeutic vaccine,” that is designed to treat people who already have a disease. As of 2010, there are only a few approved therapeutic vaccines, including one for multiple sclerosis and one for advanced prostate cancer in men.
Is There a Vaccine for HIV?
No. There is currently no vaccine that will prevent HIV infection or treat those who have it.
Why Do We Need an HIV Vaccine?
More people today have access to life-saving antiretroviral therapy for HIV/AIDS than ever before. Yet for every person who begins treatment for HIV infection, two to three others become newly infected. Treatment alone will not curtail the HIV/AIDS pandemic. To control and ultimately end this pandemic, we need a powerful array of proven HIV prevention tools that are widely accessible to all who would benefit from them.
Vaccines historically have been the most effective means to prevent and even eradicate infectious diseases. They safely and cost-effectively prevent illness, disability and death. Like smallpox and polio vaccines, a preventive HIV vaccine could help save millions of lives.
Developing safe, effective and affordable vaccines that can prevent HIV infection in uninfected people is the best hope for controlling and/or ending the AIDS epidemic.
The long-term goal is to develop a vaccine that is 100% effective and protects everyone from getting infected with HIV. However, even if a vaccine only protects some people, it could still have a major impact on the rates of transmission and help in controlling the epidemic. A partially effective vaccine could decrease the number of people who get infected with HIV, further reducing the number of people who can pass the virus on to others.
An HIV vaccine may also be beneficial for HIV-infected individuals by helping to delay the onset of AIDS or slowing disease progression. These types of vaccines are referred to as “therapeutic” vaccines. It is not known if a preventive HIV vaccine will have a therapeutic benefit in HIV-infected individuals. This would require additional clinical trials in those populations.
Why Don't We Have an HIV Vaccine Yet?
Researchers from around the world have been working for more than two decades to create a vaccine that will protect people against HIV infection. Here in the United States, the National Institute of Allergy and Infectious Diseases (NIAID) at NIH has enrolled more than 28,000 volunteers in more than 117 HIV vaccine clinical trials that have tested more than 70 different possible vaccines. The CDC and the U.S. Military HIV Research Program are also engaged in vaccine research. Scientists believe that an effective preventive HIV vaccine is possible and are building on what has been learned so far and working to speed up the research process.
But, so far, the search for an effective HIV vaccine hasn’t been successful. That’s because HIV doesn’t behave like the other viruses for which we already have vaccines. This makes it a lot harder to make a vaccine that works.
How Is HIV Different from Other Viruses?
In part, HIV is different from other viruses because your immune system never fully gets rid of it. Most people who are infected with a virus recover from the infection, and their immune systems "clear" the virus from their bodies. This is true even for viruses that can be deadly, like influenza.
Once your body has cleared a particular virus, you often develop immunity to it—meaning it won’t make you sick the next time you are exposed to it. We’ve known since the late 1700s that you can create immunity by exposing people to dead or weakened viruses that will protect them from deadly diseases later.
But the human body can't seem to fully clear HIV and develop immunity to it. The antibodies your immune system makes to fight HIV are not effective—and HIV actually targets, invades, and then destroys some of the most important cells in your immune system itself. This means that, over time, HIV does serious damage to your body's ability to fight disease.
So far, no person with an established HIV infection has managed to clear the virus naturally. That makes it hard to develop a vaccine, because scientists still aren’t sure how to encourage your body to fight HIV once it's infected.
For more information about the challenges related to developing an HIV vaccine, see Dr. Anthony Fauci's Why There Is No AIDS Vaccine. Dr. Fauci is the Director of NIH's National Institute For Allergy And Infectious Disease (NIAID).
What’s the Latest on HIV Vaccine Research?
Scientists are continuing to create and test HIV vaccines—in the lab, in animals, and even in human subjects. These vaccine trials help researchers to learn whether a vaccine will work and if it can be safely given to people.
In 2009, researchers published findings from an HIV vaccine trial in Thailand. That trial involved more than 16,000 adults and showed that a combination vaccine was safe and lowered the rate of HIV infection by 31.2%. Scientists are now trying to take what they learned from the Thai trial and make a better vaccine with greater and more definite effectiveness. For more information on the Thailand vaccine trial, see the U.S. Military HIV Research Program.
Fact Sheets & Print Materials
- NIAID – FAQs for Potential Volunteers in HIV Vaccine Research
- NIAID – HIV Vaccine Questions and Answers for HIV Treatment Advocates
- NIAID – HIV Vaccine Questions and Answers for HIV Prevention Workers
Related Topics on AIDS.gov
Frequently Asked Questions
How can I participate in an HIV vaccine trial?
For more information about HIV vaccine trials, check out Be The Generation.
Can I get HIV from participating in a vaccine clinical trial?
No. You can’t get HIV infection from participating in a vaccine trial because the vaccines being tested do not contain the virus itself.
Last revised: 02/09/2012