The first test of a new vaccine against dengue seems to have been successful, a paper published on March 16 in the journal Science Translational Medicine reveals. The paper titled “The live attenuated dengue vaccine TV003 elicits complete protection against dengue in a human challenge model” discusses the results of a Phase II trial. In a double blind trial, the 21 subjects who received the vaccine proved to be immune to dengue virus 2 when exposed. The 20 who were not immunized showed signs of illness on exposure to the virus.
The vaccine being tested is a live attenuated mix of the four serotypes of dengue. The mix has been attenuated, or weakened, so as to produce an immune response in subjects but not a clinical infection. The trial required that the 41 subjects agree to be exposed to dengue after being vaccinated with either a placebo or the vaccine.
Dengue is a serious, mosquito borne infection. It can be fatal, especially in children. The risk for a serious infection also increases sharply when a patient contracts a second, third or fourth serotype of the virus after recovering from dengue. Recovery provides permanent immunity from the serotype the patient contracted. It also provides temporary immunity to the other three serotypes.
That temporary immunity wanes and a person can, conceivably, contract another serotype and then another. A patient could have suffered four separate dengue illnesses, and the severity of second through fourth infections is markedly increased.
Dengue is transmitted by female Aedes aegypti mosquitoes. The female becomes infected through biting a person with the illness, and then can transmit it to uninfected people as it bites to obtain blood for reproductive purposes. This mosquito feeds almost exclusively on humans and is the mosquito vector for a large number of illnesses. Ae. aegypti can transmit yellow fever, all four serotypes of dengue, chikungunya and Zika as well as others.
The volunteers for this study risked contracting dengue in an effort to ensure the development of a vaccine. The success of this small study has resulted in a larger, phase III, study being implemented in Brazil on Feb. 22, according to the Washington Post on March 17. The National Institutes of Health report that Brazil reported over 1.5 million cases of dengue in 2015.
Small local outbreaks of dengue have occurred in the United States. In 2005, an outbreak of dengue was experienced in south Texas. South Florida has seen several outbreaks with the largest being in 2014. Hawaii is experiencing an on-going dengue outbreak at this time, with a total of 261 cases.