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The HIV Vaccine Trials Network began clinical trials for a potential HIV vaccine called HVTN 100 in South Africa this February. Scientists believe the key to eradicating HIV is finding a vaccine to prevent the spread of the virus.

Vaccines are made by modifying the genes of weakened viruses to produce antibodies. These genes are then carried into a host cell by the virus and incorporated into the cell’s genome, which directs the cell to produce the new antibodies. When the real virus arrives, the immune system releases these antibodies which prevent infection.

Unlike other viruses, HIV has been particularly difficult to eradicate due to its ever-mutating nature and ability to circumvent the immune system. HIV hides from the immune system by inserting its genetic material into human cells and using the host cell’s DNA to replicate billions of copies of itself. HIV also has several unique subtypes that are constantly changing, making it difficult to kill with just one type of antibody, unlike other viruses.

 The HVTN 100 trial enrolled 252 healthy HIV-free heterosexual adults between the ages of 18 and 40. The vaccine includes a combination of two experimental vaccines: a canarypox-based vaccine called ALVAC-HIV and a gp120 protein subunit vaccine designed to enhances the body’s immune response against HIV infection. The study will be double-blind. 210 volunteers will receive the vaccine, and 42 volunteers will receive a placebo.

The trial is based on the RV144 clinical trial in Thailand, which had modest but groundbreaking results. The trial included 16,000 participants who were at high risk of exposure to the virus. They found the vaccine had a protective effect for 60% of participants in the first year and 31% after 3.5 years. However, the results were not great enough for the vaccine to be put on the market.

While trials in Thailand were promising, they were not effective enough to be warranted a success.

Image Source: Paula Bronstein

A vaccine must demonstrate at least a 60% long-term prevention rate for it to be approved for use. Although 60% seems low, researchers estimate that just a 50% prevention rate in an HIV vaccine could cut the number of HIV infections in the developing world by more than half within 15 years.

In this upcoming HVTN 100 trial, they modified the vaccine for HIV subtype C strains, the most common subtype found in South Africa, and are testing variations and timing of dosage to increase the vaccine efficacy. The trial will also include booster shots at the one-year mark to try to prolong the early high protective effect observed in RV144.

The results are expected to be released in two years. If successful, it will pave way for larger clinical trials in the future and bring us closer to understanding the HIV virus and creating a vaccine.

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