The dengue fever ward at the Hindu Rao Hospital in New Delhi, India. The WHO estimates that 500,000 people are hospitalised with severe dengue every year, many of them children. 2.5 percent of that number die Saumya Khandelwal/Hindustan Times via Getty Images

An experimental vaccine against the dengue virus has been found to protect 100 percent of recipients in a clinical trial carried out by the USA's National Institute of Allergy and Infectious Diseases (NIAID).

In the NIAID trial 21 people were vaccinated with TV003, while 20 received a placebo. Six months later they returned to be infected with a mild version of dengue-2. All 21 people who'd received the vaccine were protected against infection. All 20 members of the placebo group contracted dengue. A modified version of the vaccine is now being developed in an attempt to treat the related Zika virus.


TV003 is a live attenuated vaccine, meaning that, like measles, mumps, and flu vaccines, it's made by creating a greatly weakened version of the virus it's designed to combat. Specifically, this vaccine involves a combination of four recombinant dengue vaccine candidate viruses, designed to combat all four major dengue virus serotypes.

The volunteers who received the vaccine experienced no ill effects from it and developed only a mild rash, which they didn't notice and which vanished entirely in five to ten days. All subjects successfully developed antibodies against dengue.

Dengue virus is related to Zika and both are primarily spread by the Aedes mosquito. There are four major dengue serotypes - related strains that can be distinguished by their cell surface antigens - plus a recently classified fifth strain only known to have caused one infection. Dengue is widespread in tropical and subtropical regions, including large parts of Africa, Central and South America, Asia and the Caribbean.


Human challenge studies of this kind, in which volunteers are exposed to disease-causing pathogens under highly controlled conditions, are an important tool for testing the viability of vaccines on a small scale before carrying out larger, most costly trials. Such trials can only safely be carried out using viruses that are known to have mild effects, such as this version of dengue-2.

Stephen Whitehead, Ph.D., of the NIAID, developed the dengue-2 challenge virus used in this trial by genetically modifying a dengue-2 serotype virus that was isolated in the Kingdom of Tonga in 1974. The original virus was notable for causing only mild illness, and previous tests have shown that the challenge virus causes recipients to develop viremia, the presence of virus in the blood, but with only a mild rash as its worst symptom.

Clinical trial lead Dr Anna Durbin said that "We were pleasantly surprised to see that this candidate vaccine provided complete protection in everyone who received it. The dengue-2 serotype is considered the relatively weaker component in this, and other, candidate dengue vaccines, so its ability to confer protection from a challenge with dengue-2 virus was encouraging." "The findings from this trial are very encouraging to those of us who have spent many years working on vaccine candidates to protect against dengue, a disease that is a significant burden in much of the world and is now endemic in Puerto Rico," said Whitehead. "In fact, these results informed the recent decision by officials at Brazil's Butantan Institute to advance the TV003 vaccine into a large phase 3 efficacy trial."