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During a clinical trial of 48 participants, 100% of those that received the TV003 vaccine were protected from infection.
A National Institutes of Health (NIH) clinical trial, during which volunteers were infected with the dengue virus for six months and then given either an experimental dengue vaccine or a placebo injection, proved 100% effective, NIH said in a March 16, 2016 press announcement. All 21 volunteers who received the vaccine, TV003, were protected from infection, while all 20 placebo recipients developed dengue. The study was published in Science Translational Medicine.
Dengue fever, prevalent throughout the tropics and subtropics, is caused by four related dengue viruses-called serotypes-that are spread by Aedes mosquitoes, the same mosquitoes that spread Zika virus. Most of the estimated 390 million people who are infected with dengue virus each year develop either no symptoms or a mild illness. However, some people develop serious or life-threatening illness, and large outbreaks lead millions to seek care.
Stephen Whitehead, PhD, and his colleagues from NIH’s National Institute of Allergy and Infectious Diseases (NIAID) primarily developed the experimental vaccine. FDA’s Center for Biologics Evaluation and Research also contributed to the development. The candidate vaccine was created from a mixture of four live, weakened (attenuated) viruses targeted to each of the four serotypes. A total of 48 healthy adult volunteers enrolled at two trial sites, the University of Vermont College of Medicine and Johns Hopkins Bloomberg School of Public Health participated in the study. Participants were randomly assigned to receive either vaccine or placebo injection.
Whitehead and colleagues also developed the challenge virus used in the trial, which is a genetically modified version of a dengue-2 serotype virus isolated in the Kingdom of Tonga in 1974. The original virus was notable for causing only mild illness. In previous human challenge trials with this modified virus, Whitehead and his co-investigators established the virus dose that would cause all recipients to develop viremia-the presence of virus in the blood-and most to develop a mild rash. According to Whitehead, by inducing only rash (without fever) in the majority of recipients, the challenge virus mimics natural dengue virus infection, which often features such a rash.
In the study, all 20-placebo recipients developed viremia, 16 (80%) developed mild rash and 4 (20%) had a temporary drop in white blood cell count following challenge with the virus. None of the 21 TV003 vaccine recipients developed viremia or any other sign of infection after challenge.
Whitehead is currently developing a human challenge model using a modified dengue serotype-3 virus. This challenge virus could be used in future clinical trials to test the efficacy of candidate dengue vaccines or therapies.