Scientists have launched a large-scale clinical trial – which hopes to enroll 17,000 healthy individuals – to test a vaccine’s ability to prevent dengue fever.

The experimental TV003 vaccine, developed by scientists at the National Institute of Allergy and Infectious Diseases (NIAID), is entering a placebo-controlled, multi-center Phase 3 trial using test vaccine created in the Brazilian capital Sao Paulo.

NIAID Director Dr. Anthony Fauci said researchers spent years developing and testing candidate dengue vaccines designed for producing antibodies against all four serotypes of the virus: DEN-1, DEN-2, DEN-3 and DEN-4, all transmitted by the Aedes aegypti mosquito.

Earlier trials conducted in the U.S., he added, showed promise in inciting a strong immune response after a single dose alone.

“Because the impact of dengue fever in Brazil is especially large and the country has an excellent health infrastructure, it is an ideal location to test the vaccine candidate,” explained Dr. Fauci.

Dengue fever commonly occurs in tropical countries, with about half the global population at risk of being infected. According to the World Health Organization, up to 400 million dengue infection cases take place every year, leading to 500,000 hospitalizations.

In Brazil last year alone, over 1.5 million dengue cases were reported.

When one is exposed to a dengue virus type, he or she gains immunity from the said type, but not to the other three. In fact, a second dengue infection with a different type can be more serious.

This development came on the heels of the Zika virus outbreak in Brazil and other nations in the Americas, which prompted a travel advisory for pregnant women planning to travel to the 14 affected countries.

Zika’s arrival in Brazil has coincided with a rise in documented cases of microcephaly, a birth defect marked by severe defect – underdeveloped heads and brains – or death in babies.

Dengue and Zika are cousin viruses spread by the same mosquitoes. But while Zika and another cousin, chikungunya, rarely lead to serious illness, dengue can result in fatal, hemorrhagic fevers accompanied by body aches and complications leading to bleeding and shock.

The new dengue vaccine trial intends to recruit nearly 17,000 healthy people from ages 2 to 59. Two-thirds of them will receive a single vaccine dose, while the remaining one-third will be given a placebo.

Volunteers will be monitored for five years, with researchers hopeful to get insight into the vaccine’s efficacy in less than two years.

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