A viral is the same piece of content that is passed from person to person. The content is 'static'
e.g Vanilla Ice Sorry
A meme is an idea/piece of content that is remixed and passed from person to person. The content is 'fluid'.
Memes are superior because they usually have a longer shelf life as people can keep changing them and the peer who passes them on can help effect the content and has a vested interest in the outcome.