It doesn't exist, it's just a 'make it look like we are doing something' method. But that being said although not 100% effective, they must reduce the risk (when used correctly), even if it is only slightly. I do not want to wear a mask, but I do because it is the law at the moment. If it makes people feel safe and gets them out, and in turn the economy moving, surely it is a good 'bad' thing.