Dengue fever vaccine shows promise

US scientists at the National Institutes of Health say their dengue vaccine is safe and stimulates a strong immune response in most recipients. 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 global burden of dengue is enormous and it is growing," Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, part of the NIH, said in a statement. "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 World Health Organization estimates 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, Fauci said. Infection with one dengue virus results in immunity to that specific virus but not to the other three, but research showed the likelihood of severe disease increases when a person is subsequently infected with a different dengue virus -- suggesting the ideal dengue vaccine would be protective against all four dengue viruses, the study said. The Phase I clinical trial, led Dr. Anna Durbin 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 final study analysis included 112 healthy men and women ages 18-50, who had not previously been exposed to dengue or related viruses. Participants were randomized into four groups -- in each group, 20 volunteers received a single 0.5-milliliter injection of one of the four candidate vaccine combinations, and eight received a placebo. The study, published in the Journal of Infectious Diseases, found all four candidate vaccine combinations induced antibody responses against each of the dengue viruses, but one combination -- TV003 -- appeared to induce the most balanced antibody response against the dengue viruses.