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The Basics

This fact sheet provides basic information on preventive HIV vaccines. For additional materials on the status of HIV vaccine research, visit our HVAD section. For more basic fact sheets in this series on emerging HIV prevention strategies visit www.avac.org/intro.

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What is an HIV vaccine?

Researchers are working to come up with two kinds of vaccines against HIV. One kind, a preventive vaccine, would reduce HIV risk in people who are HIV-negative. It would teach their immune systems (made up of cells and substances that protect the body) to spot the virus right away if exposed to it (for example during sex), and block it from causing an infection. No licensed preventive HIV vaccine exists yet.

The other kind is a therapeutic HIV vaccine. People living with HIV would take it to help make their immune systems stronger and better able to control the virus. This kind of vaccine could, in theory, help people control the virus without antiretroviral drugs, or be used as a supplement to antiretroviral treatment (ART) regimens. Research on therapeutic vaccines may also help in research on how to cure HIV. No therapeutic HIV vaccine has been proven to work yet.

This fact sheet is about research to find preventive vaccines for use by HIV-negative people.

How does HIV vaccine research happen?

Vaccine research starts in the lab where scientists develop vaccines they believe have promise. Next, the candidate vaccines are tested on animals. If a vaccine shows evidence of safety and potential efficacy in animals, it can move on to testing in humans. This starts in small trials and, if results show the vaccine is safe and causes good immune responses, it can move to larger human trials. The large trials are called efficacy trials, and named Phase IIb or Phase III trials. Thousands of volunteers are needed to participate in these trials. Without them, it would be impossible to find out if the test vaccine lowers people’s risk of getting HIV. To learn more about how HIV prevention trials work, download AVAC’s fact sheet, HIV Prevention Trial Terms: An Advocate’s Guide.

What is happening in HIV vaccine research now?

Two HIV vaccine candidates are currently being tested in large-scale efficacy trials. One is a Phase IIb/III trial called HVTN 702, or Uhambo, enrolling 5,400 South African men and women. At least 12 clades (also called strains or sub-types) of HIV exist in the world. HVTN 702 is testing a vaccine designed to prevent clade C, the most common HIV clade in Southern Africa.

The second trial is called HPX2008/HVTN 705, or Imbokodo, and is a Phase IIb trial enrolling 2,600 women in five countries across sub-Saharan Africa. The test vaccine in the Imbokodo trial is known as a mosaic vaccine. It is designed to protect against multiple HIV clades. A Phase III efficacy study of this same vaccine regimen is in the planning stages.

A third vaccine trial program, known as PrEPVacc, has started to gather data on HIV risk and other demographic data, in preparation for a Phase IIb clinical trial that will test two combination regimens each containing multiple clades. The clinical trial is expected to begin in early 2020, enrolling 1,688 men and women from general and key population groups in four African countries.

What are the discoveries in HIV vaccine research so far?

In 2009, a trial in Thailand called RV144 showed that volunteers who got the test vaccine were 31 percent less likely to get HIV during the trial than those who got the placebo. The vaccine was also safe and well-tolerated. The RV144 results showed that the vaccine protected some of the trial’s volunteers from HIV. Since that trial, researchers have identified some of the immune responses that might have led to protection. They have also come up with adjustments that they think will improve the vaccine and adapted it for use in other parts of the world. The Uhambo trial (HVTN 702), described above, uses updated versions of the components found in the RV144 vaccine strategy.

In addition to the larger-scale studies described above, scientists are working on many different vaccine candidates and strategies that are in earlier, smaller human trials and pre-clinical studies. See the latest updates in our HIV Vaccine Research Pipeline graphic.

How is antibody research helping us advance HIV vaccine research?

Antibodies play a big part in fighting off disease. Certain types of antibodies, known as broadly neutralizing antibodies (bNAbs), might be very useful to HIV prevention (and treatment and cure, too). They are Y-shaped proteins made by B cells (immune cells). They can attach themselves to a certain part of HIV’s surface and stop it from infecting healthy cells. “Broadly neutralizing” means that this type of antibody can recognize and attach to multiple HIV clades that exist around the world.

It takes a long time after HIV infection for a person’s body to produce bNAbs and many people never produce them. Scientists sometimes say that, “Today’s antibodies can neutralize yesterday’s virus.” Antibodies against any pathogen go through a series of changes that make them better and better at finding and blocking a given invader. This “maturation process” can take many months or years. Scientists hope to develop a vaccine or series of vaccines that would coach the body through this antibody maturation process, in the absence of an infection.

bNAbs are also being studied for antibody-mediated prevention using a method called passive immunization. With passive immunization, bNAbs are brought into the body through an infusion. Once there, these bNAbs might be able to prevent HIV infection. However, since it wouldn’t be the body making the antibodies, the levels of infused bNAbs—and any protection they might provide against HIV—would diminish over time. Two large clinical trials testing this idea are now fully enrolled and ongoing in the Americas, Europe and across sub-Saharan Africa. Called the Antibody Mediated Prevention (AMP) studies, these trials are testing the safety and efficacy of the broadly neutralizing antibody VRC01 for HIV prevention.

A growing number of antibodies are going through animal testing and smaller, early-phase clinical trials. In future trials, researchers hope to test those that are especially strong and long-lasting, as well as combinations of antibodies. They will also test other ways of introducing bNAbs to the body, such as with an injection. For an ongoing list of bNAbs as they are discovered, visit www.bnaber.org. For more details about bNAb research, check out our P- Values blog on The Rise of Broadly Neutralizing Antibodies as well as our two latest infographics on the bNAb pipeline and combination studies.

Last updated May 2019.