Stevia is a sweetener from the extraction of a plant called stevia. This has become famous as a non-caloric sweetener to reduce calories and food manufactures have wanted to make the most of this. They also need to counter the bitter after taste in some drinks.
This announcement to use the new sweetener in Sprite was made at a perfect timing just before the airing of Coca-Cola's anti-obesity TV ad in the United Kingdom. In the US, this advertisement did raise a storm, especially since everybody knows the role sodas play in increasing obesity rates.
Source: Medindia