IAVI Responds to the Announcement that Merck's AIDS Vaccine Candidate Trial Demonstrated a Lack of Efficacy

September 21, 2007

Though the outcome is disappointing, IAVI urges the field to maintain hope and embrace innovation 

Sponsors of the STEP study, testing Merck & Co’s MRK-Ad5 AIDS vaccine candidate, announced September 21 that they have discontinued the Phase IIb trial based on an interim analysis that concluded that the product was not efficacious. The trial was sponsored by Merck and the HIV Vaccine Trials Network (HVTN) and funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.  

The news is a letdown, particularly since the MRK-Ad5 product was widely thought to be one of the most promising vaccine candidates to advance into human testing. However, International AIDS Vaccine Initiative (IAVI) President and CEO Seth Berkley stressed that scientists and activists in the field should not be discouraged. 

“While the results of the Merck trial are disappointing,” said Berkley, “this outcome should not demoralize those of us who are committed to the battle against AIDS. Devising an AIDS vaccine has proved far more difficult than many of us imagined. But we must face that fact and ask ourselves constantly, how can we do better, knowing, as we do, that a vaccine is the key to ending this terrible pandemic.” 

Berkley added that the field owes a debt of gratitude to the volunteers who participated in the STEP trial, and to the sponsors of the study. He praised Merck & Co. for its exemplary commitment to the search for an AIDS vaccine, an enterprise many in industry have declined to join because of the high financial risks. 

After concluding some four years ago that the first-generation vaccine candidates already in the pipeline would provide partial efficacy at best, IAVI began shifting more of its resources toward addressing some of the critical scientific questions hampering AIDS vaccine designers. The organization expects its investments to produce improved vaccine candidates in coming years. IAVI has invested in particular in the promising field of replicating vectors and in its Neutralizing Antibody Consortium (NAC). The NAC is a global collaboration of scientists working to design an AIDS vaccine that would activate the antibody arm of the immune system, rather than the T-cell arm, which is the basis of most vaccine candidates now in the pipeline, including the Merck product. 

“We believe these kinds of innovation are the best answer to disappointments like the Merck trial results,” said Berkley. 

The results of the STEP trial will require further study. IAVI may need to recalibrate its Research and Development program further on the basis of the final analysis. For the time being, the organization has already heard from NIAID that it is reviewing the data from the Merck trial to ensure that the design of its upcoming PAVE trial, in which IAVI plans to participate, remains appropriate. This trial, in Africa and the Americas, will test a candidate, DNA/rAd5, with some similarities to Merck’s. IAVI had been planning to begin a supporting trial, a phase II test of the same candidate, in Africa soon, but will delay that start until more information is available about the relevance of the Merck results. 

“HIV is a tough adversary, and there will inevitably be more setbacks, but with perseverance the world will find a vaccine,” said Berkley. “Success will require the best science, and a sustained commitment, from industry, academia, government and donors.” “IAVI,” he added, “will continue, steadfastly, to bring those partners together in an effort to help end the AIDS pandemic.”

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