Nov. 8, 2007 The new analyses revealed from the STEP HIV vaccine clinical trial are both disappointing and puzzling. At this time, the data offer no clear explanations as to why the vaccine showed no measurable efficacy or why among individuals with background immunity to the adenovirus vector, there were more HIV infections in the vaccinees as compared to those in the placebo group. Analyses of the STEP data are continuing, and it will take some time before we fully understand these results.
NIAID and its study partners, Merck & Co., Inc., and the HIV Vaccine Trials Network (HVTN), fully recognize the importance of these results to the volunteers who participated in the study and the larger scientific community.
The failure of this HIV vaccine product was a disappointment. But this setback should not and can not diminish our commitment to developing an effective HIV vaccine. Every day, another 12,000 people become infected with HIV, most of whom live in resource-poor countries. Approximately, 40 million people are currently living with HIV infection, and more than 25 million people with AIDS have died. Last year alone, an estimated 4.3 million new HIV infections occurred worldwide.
Historically, vaccines have been the most effective weapon against infectious diseases, such as polio, measles, mumps and smallpox. The goal of developing a safe and effective HIV vaccine is a key goal of HIV research today. However, the complex and unique nature of HIV has presented a formidable challenge to developing an effective vaccine.
In the absence of an HIV vaccine, there are proven methods for preventing HIV transmission that we, as a global community, must implement on a wider scale. These methods include HIV/AIDS education and behavior modification; condom usage to prevent sexual HIV transmission; medically supervised adult male circumcision in appropriate settings; needle exchange programs to curb bloodborne HIV transmission among injection drug users; and the use of antiretroviral drugs in HIV-infected pregnant women to prevent mother-to-child HIV transmission.
Although none of these interventions is completely effective on its own, when used in combination they can have a significant impact on HIV prevention. Less than 20 percent of the world's population currently has access to proven HIV prevention services, but this figure is growing with the efforts of programs such as the President's Emergency Plan for AIDS Relief, the Global Fund to Fight AIDS, Tuberculosis and Malaria, and many others.
"It is also important to recognize that the failure of the Merck product to prevent HIV infection is not unexpected. Merck's candidate, like nearly all vaccine candidates now in the pipeline, was designed to activate the T-cell arm of the immune system. T-cells work like commando units, travelling through the body, seeking out pathogen-infected cells, which they then kill. Because T-cells only attack cells that are already infected, many scientists, including those at IAVI, think T-cell vaccines are unlikely to protect individuals from becoming infected. It's more likely T-cell vaccines will reduce the amount of virus in people who, once vaccinated, become infected. In the event, the Merck vaccine did not achieve either result, said Dr. Seth Berkley, President and CEO of The International AIDS Vaccine Initiative.
He continued, "Because of this limitation of T-cell vaccines, some scientists in the field, including those at IAVI, in recent years have shifted more resources toward discovery of next-generation candidates, including those that would activate the antibody arm of the immune system. Antibodies act like the body's border guards, stopping pathogens from entering the body, and thus preventing infection."
In addition to existing HIV prevention tools, scientists must create new, evidence-based approaches to HIV prevention, such as topical anti-HIV gels or creams that could be applied prior to sexual intercourse; preventive regimens of antiretroviral medications; and, especially, a vaccine. A setback in a given clinical trial is no reason to lessen our commitment to tackling the scientific challenges inherent in this field of research. What is learned from the STEP study will inform ongoing and future HIV vaccine research.
Researchers must regroup and recommit to developing an HIV vaccine and other new prevention weapons while providing proven HIV prevention tools to those who need them. In the global fight against the HIV/AIDS pandemic, every prevention tool is of paramount importance.
Dr. Fauci is director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health in Bethesda, Maryland.
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