According to the BBC, now mosquitoes can purposely be infected with a natural virus that out-competes Dengue fever:

The bacteria Wolbachia is found in 60% of insects. It acts like a vaccine for the mosquito which carries Dengue, Aedes Aegypti, stopping the Dengue virus multiplying in its body.

Wolbachia also has an effect on reproduction. If a contaminated male fertilises the eggs of a female without the bacteria, these eggs do not turn into larvae.

If the male and female are contaminated or if only a female has the bacteria, all future generations of mosquito will carry Wolbachia.

As a result, Aedes mosquitoes with Wolbachia become predominant without researchers having to constantly release more contaminated insects.

In Australia this happened within 10 weeks on average.

A statistic that caught my eye:

Brazil leads the world in the number of Dengue cases, with 3.2 million cases and 800 deaths reported in the 2009-2014 period.

Doing the math, that adds up to a death rate of 0.025%.