There are many types of vaccines, but all generally work by teaching the immune system to recognize and eliminate a disease-causing microorganism. Some vaccines are designed to help the immune system prevent an infection and are called preventive vaccines. Other vaccines are designed to help people who are already infected to clear the infection and are called therapeutic vaccines. Currently, there are no effective HIV vaccines of either kind.
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Studies at the HVTN focus on preventive vaccines. Vaccines used in HVTN studies are made in the lab. Because we do not use the actual virus, you cannot get an HIV infection from being in one of our studies (see How Vaccines Work)
Some of the types of vaccines that are being studied currently are described below. In addition to vaccines that teach your body to fight HIV, some HVTN studies involve other HIV prevention products. These studies help scientists learn more about how vaccines can work either alone or in combination with other HIV prevention tools. It’s all part of our goal to find the most effective vaccination strategy to prevent HIV infection.
Proteins are natural substances. They help build and maintain your body, and they do the same for viruses such as HIV. A protein vaccine may be made of tiny lab-made pieces of proteins that look like pieces of the HIV virus (a peptide vaccine), or it may be made of bigger pieces (a subunit protein vaccine). These proteins do not actually come from real HIV. It is like using a photocopy, not the original.
After vaccination, the body’s immune system may respond to the proteins in the vaccine. If a vaccinated person is exposed to HIV in the future, the immune system may recognize the same proteins in HIV and fight the virus.
A DNA vaccine uses copies of a small number of HIV genes, which are inserted into pieces of DNA called plasmids. The HIV genes will produce proteins very similar to the ones found in real HIV. After vaccination, the body’s immune system may respond to the HIV-like proteins, and fight the real virus if the vaccinated person is later exposed to it.
Viral vector vaccines
For a viral vector vaccine, non-HIV viruses are used to carry genes that tell the body to make some HIV proteins. These viral vectors don’t cause disease in people. The genes are inserted into the vector, which carries them into the body's cells. Then, as with a DNA vaccine, the HIV genes will tell the body to make proteins like the ones found in real HIV. After vaccination, the body’s immune system may respond to the proteins, and fight against HIV if a person is infected in the future.
One example of a viral vector that has been used in research so far is the canarypox virus vector. The canarypox virus causes canarypox, a disease in birds that is distantly related to smallpox. Because the canarypox virus does not cause illness in people, using this virus to make a viral vector vaccine was expected, and so far appears to be very safe. A canarypox virus vector was made in the lab with copies of HIV genes instead of some of the canarypox virus genes. This vaccine was tested together with a protein vaccine in a study called RV144 that was performed in Thailand and had promising results. The vaccines in the study prevented some HIV infections. Scientists are now trying to learn how this vaccine worked and how to improve it.
Non-vaccine prevention modalities
Recent findings have identified new methods that can help reduce a person’s risk for HIV infection. Because the new methods that have been found so far are only partially effective, HVTN scientists are working on ways to combine vaccination with these new non-vaccine prevention methods to hopefully achieve maximum effectiveness for preventing HIV infection.
One example of a new HIV prevention method is pre-exposure prophylaxis, or PrEP. For PrEP, people who do not have HIV take a daily dose of anti-HIV medication to keep them from becoming infected. The medication stops HIV from copying itself in a person’s cells after they have been exposed and prevents them from becoming sick. Because it is important to see how a vaccine might work with PrEP to prevent HIV infections, some HVTN vaccine studies may include PrEP.