All it takes is one bite: Dengue is a debilitating virus that’s transmitted to humans by the bite of an Aedes aegypti mosquito that has previously bitten a person infected with the dengue virus.
Half of the world’s population is at risk of catching dengue, which is currently the fastest growing of all mosquito-borne tropical diseases. It’s now estimated by the World Health Organizations that more than 50 to 100 million people in more than 100 countries develop the acute illness each year, primarily in tropical and subtropical areas of Southeast Asia, Africa, and Latin America.
Dengue fever has now made its way to previously unaffected areas, including Japan and India, as well as Puerto Rico, the U.S. Virgin Islands, and parts of Florida and the Texas-Mexico border. With its recent appearance in Portugal, the current fear is that climate change could help spread dengue to southern Europe.
There is considerable cost to dengue, including medical care and lost wages and decreased productivity. Dengue sufferers typically experience high fever, rash, headaches, convulsions, and joint and muscle pain that can last up to two weeks. In severe cases, hospitalization is needed, especially for children, but the disease still proves fatal for 20,000 people each year.
The biology of dengue is complex and has baffled researchers for decades. The disease currently has no cure, and despite the huge number of sufferers, there is no effective drug or vaccine treatment. A primary difficulty is that a vaccine would have to prevent four different but closely related viruses simultaneously—serotype 1, 2, 3, and 4. And while people can get infected with any virus, or all of them, immunity against one serotype does not provide immunity against any of the other three. Moreover, the prevalence of serotypes varies from region to region around the globe.
The world’s first vaccine against the dengue scourge has now been developed and tested. The vaccine worked in just-completed Phase III trials of children 2 to 14 in five areas across Asia. Almost 60 percent of the 6,000 children were protected against the disease compared to placebo injections after a three-shot, two-year period.
Protection against serotypes 3 and 4 was 75 percent; against serotype 1 efficacy was 50 percent, while efficacy against serotype 2 was 35 percent. However, this promising vaccine—more than 20 years in development—had its greatest impact on the most severe forms of the disease by reducing the number of people needing hospitalization. Hemorrhagic fever, a potentially life-threatening complication for children less than ten years of age, was also reduced by 80 percent.
In similar trials conducted in Latin America with the vaccine, more than 20,000 children aged 9 to 16 in Brazil, Colombia, Honduras, Mexico, and Puerto Rico achieved similar protective advantages against dengue as did children in the Asian studies.
While these vaccination reductions in dengue fever are considered moderate, they can still translate into a huge benefit for countries plagued by the disease in terms of medical costs, work productivity, and human suffering.
As the dengue threat increases, other dengue vaccines are currently in development and undergoing clinical trials, including one that that immunizes against all four dengue virus serotypes. However, these vaccines will not be available before 2017, at the earliest.
In the meantime, the current vaccine is expected to be submitted to regulatory groups in early 2015, with commercialization expected later in the year.
Where Are They Now
After 20 years of research, the dengue vaccine will be made commercially available in the Philippines starting October 2015, with the potential to save the Philippian government $8.2 billion per year. Commercialization is expected to follow in 2015 and 2016 for other countries where dengue hits hardest.