NIH's candidate vaccine safe in treating dengue

Published on January 23, 2013 at 11:23 PM · No Comments

A candidate dengue vaccine developed by scientists at the National Institutes of Health (NIH) has been found to be safe and to stimulate a strong immune response in most vaccine recipients, according to results from an early-stage clinical trial sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), part of the NIH. The trial results were published online on January 17 in the Journal of Infectious Diseases.

Dengue fever, prevalent in many tropical and subtropical regions of the world, is caused by any of four related viruses-DENV-1, DENV-2, DENV-3 and DENV-4 -that are transmitted to humans by Aedes mosquitoes. The World Health Organization estimates that every year, 50 million to 100 million cases of dengue occur worldwide, resulting in 500,000 hospitalizations of patients with severe disease, many of them in children.

Infection with one dengue virus results in immunity to that specific virus but not to the other three. Research shows that the likelihood of severe disease increases when a person is subsequently infected with a different dengue virus. This observation suggests that the ideal dengue vaccine would be tetravalent-that is, protective against all four dengue viruses.

"The global burden of dengue is enormous-and it is growing," said NIAID director Anthony S. Fauci, M.D. "We are cautiously optimistic about these recent clinical trial results with this candidate tetravalent vaccine developed at NIAID; however, much more work still needs to be done."

The Phase I clinical trial, launched in July 2010 and led by principal investigator Anna Durbin, M.D., at Johns Hopkins Bloomberg School of Public Health in Baltimore, tested a single dose of each of four versions of the investigational dengue vaccine TetraVax-DV. The vaccine was developed by scientists in NIAID's Laboratory of Infectious Diseases. It is a live, attenuated vaccine, which means that the viruses it contains are weakened enough such that they do not cause illness but still can induce an immune response. Each of the four vaccines tested included different mixtures of components designed to protect against all four dengue viruses.

The Phase I study was conducted in Baltimore; Burlington, Vt.; and Washington, D.C. The final study analysis included 112 healthy men and women ages 18 to 50 years who had not previously been exposed to dengue or related viruses such as West Nile virus and yellow fever virus.

Participants were randomized into four groups. In each group, 20 volunteers received a single 0.5-milliliter subcutaneous (under the skin) injection of one of the tetravalent candidate vaccine combinations, and eight others received placebo. All were monitored for immediate adverse reactions for at least 30 minutes after vaccination, and subsequently took their body temperatures three times daily for 16 days to check for possible adverse reactions. Participants also received a physical exam every other day up to Study Day 16, and then again on study days 21, 28, 42 and 180, when blood tests were also performed.

The researchers found that all four candidate vaccine combinations induced antibody responses against each of the dengue viruses. However, one vaccine combination, TV003, appeared to induce the most balanced antibody response against the dengue viruses. A single dose of TV003 resulted in an antibody response to all four dengue viruses in 45 percent of participants and against three of the four viruses in an additional 45 percent. Overall, an immune response to at least three viruses was seen in 90 percent of vaccinees given TV003.

"What is promising about TV003 is that it elicited solid antibody responses after just one dose," explained Stephen Whitehead, Ph.D., of NIAID's Laboratory of Infectious Diseases, who led the development of the vaccine candidates. "Other vaccines in development require two or three injections at higher doses to achieve similar results."

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