According to the WHO, 2.5 billion people are at risk for dengue fever, between 50 million and 100 million people contract the disease each year, and over a million people die from it each year.

For such a big health risk, you'd expect big plans to fight back. And science looks ready to deliver, with multiple approaches being used to help turn the tide.

In Brazil, where dengue fever is depressingly common (the highest incidence in the world), an intriguing pilot program has begun. In the lab, a gene is inserted into male mosquitoes that will kill them (although they are fed a temporary antidote that will keep them alive until their mission is complete); they're released into the world, mate, and pass on the gene to their offspring. The offspring die before adulthood, hopefully helping winnow down the mosquito population.

There's also another option: a dengue vaccine. Several companies are developing vaccines, chief among them best-in-class European big pharma Sanofi (NASDAQ:SNY). Sanofi has already completed a late-stage trial for its dengue vaccine, and the data look good (although we're still waiting to receive more data from another late-stage trial). And helping defeat this scourge could be big money for Sanofi, with its vaccine having the potential (if approved) to be a blockbuster drug.

In the video below, from Where The Money Is, the Motley Fool's investing show, health care analysts Michael Douglass and David Williamson discuss dengue, how we're fighting back, and Sanofi's exciting opportunity to do well by doing good.