The first study in 7 years to evaluate the efficacy of an HIV vaccine has begun in South Africa. The Phase 2b/3 HVTN 702 study is testing a new version of the only HIV vaccine candidate which has previously shown some protection against HIV infection. The study plans to enroll 5,400 South African adults aged 18–35 years who are HIV-uninfected and sexually active.

The investigational vaccine regimen is based on the one studied in the RV144 clinical trial in Thailand that was headed by the U.S. Military HIV Research Program and the Thai Ministry of Health. In 2009, data from RV144 demonstrated for the first time that a vaccine could prevent HIV infection though only modestly. Specifically, the vaccine was 31.2% effective at preventing HIV infection over a 3.5 year follow-up post-vaccination.

Interim results from HVTN 100 (n=252), a previous clinical trial, had found that the new vaccine regimen was safe for the study participants and resulted in comparable immune responses to those reported in RV144. 

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The new HVTN 702 vaccine regimen has been adapted to be specific for HIV subtype C, which is predominant in southern Africa. It consists of two experimental vaccines: ALVAC-HIV (Sanofi Pasteur), a canarypox vector-based vaccine, and a 2-component gp120 protein subunit vaccine with an adjuvant (GlaxoSmithKline) to boost the body’s immune response to the vaccine; the adjuvant, MF59, differs from that used in RV144. The regimen also includes booster shots at 1 year in order to extend the early protective effect seen in RV144.

In addition to the modified vaccine regimen, the study’s design, schedule, and parts of the RV144 vaccine regimen have been altered to hopefully achieve greater and more sustained vaccine-elicited protective immune responses. Study patients are being randomized to receive five injections of either the experimental vaccine regimen or placebo over 1 year. Those who become HIV-infected will be referred to local healthcare providers and will receive counseling on reducing the risk of viral transmission.

Anthony S. Fauci, MD, director of the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, added, “Even a moderately effective vaccine would significantly decrease the burden of HIV disease over time in countries and populations with high rates of HIV infection, such as South Africa.”

The study results are anticipated in late 2020.

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