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New HIV Vaccine Shows Promising Results

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With almost 37 million people worldwide living with HIV/AIDS, and an estimated 1.8 million new cases each year, the need for a safe and effective preventative vaccine is more urgent now than ever. The Lancet recently published research regarding an experimental HIV-1 vaccine regimen that has proven to be well-tolerated in healthy adults and rhesus monkeys.

This research was based on a clinical trial involving nearly 400 hundred adults, performed with the goals of determining safety and efficacy of the vaccine candidate. This regimen was developed using a “mosaic” of different HIV viruses and combining them to elicit immune responses against a variety of HIV strains. Specifically, this study demonstrated that the mosaic Ad26 prime, Ad26 plus gp140 boost HIV vaccine candidate prompted robust immune responses against HIV in humans and monkeys with similar magnitude, kinetics, phenotype and durability. Further, the candidate provided 67% protection against infection with an HIV-like virus in monkeys.

Results of the first phase of this efficacy trial showed that, of all candidates tested, the Ad26/Ad26 plus gp140 vaccine candidate induced the greatest immune responses in humans and also provided the best protection in monkeys. Specifically, the trial demonstrated complete protection against simian-human immunodeficiency virus (SHIV) infection in over two-thirds (67%) of the vaccinated animals after six challenges. Some mild adverse reactions were reported in five participants, including abdominal pain and diarrhea, postural dizziness and back pain. Additionally, the relevance of vaccine protection in rhesus monkeys to clinical efficacy in humans is not entirely clear and thus limits the interpretation of the trial.

Though the ability to induce immune responses specific to HIV strains may not indicate that a vaccine will protect humans from infection, phase 2b of the efficacy trial has been initiated and is designed to answer this exact question. This phase will follow only one other HIV vaccine concept efficacy trial that tested in humans and provided evidence of protection; the RV144 trial of 2009. A canarypox ventor prime, gp120 vaccine regimen was tested in the RV144 trial, but the resulting 31% efficacy rate was considered too low to advance the vaccine to common use. Dr. George Pavlakis and Dr. Barbara Felber from the National Cancer Institute at Frederik, Maryland, USA say: “It remains to be determined whether improved efficacy over RV144 will be achieved by the current efficacy trial . . . .” They added: “Implementation of even a moderately effective HIV vaccine together with the existing HIV prevention and treatment strategies is expecting to contribute greatly to the evolving HIV/AIDS response."