Awesome game!
First i have to say that this game is really really awesome. The theme is really cool, the premise is really cool, and the music is also really cool. Theres a few things i would point out though:
1 - it would be good to have skill levels implemented that control how much time you have available, or at least give players some more.
2 - It might be a good idea to include an option to play without the timer, and this function would serve more as a time-waster then an actual skill testing game.
3 - Something about the controls was a bit lacking, i'm not sure how you would fix it because if the viruses infected on touch it would be more of a movie then a game, perhaps you could just click the red blood cells and have the nearest virus instantly infect it.
And in future sequels to the game if they are created:
1 - Maybe include different types of cells to infect that create different types of viruses (i.e. maybe skin cell viruses would be tougher?)
2 - Having a storyline to it if that would be at all possible, perhaps even have some organized destruction of various body parts/systems, i.e. first level might be destruction of the liver system, and there could be a boss of sorts in which you drag viruses into the liver or something like that whilst chemicals and things other then white blood cells (which would be present) are thrown at you. I'm not sure i just think that sounds pretty cool
overall this game rules though, i have played it for about 3 hours now and will continue to play it for many more.