Ive been pondering recently about how I'm going to go about showing the virus appearing, I really want to add a sense of drama to the situation and some blue blobs falling out the sky doesn't exactly seem threatening to me. For the moment when it arrives into the scene I think I'm going to go the 2D route.
Here's how the sequence will go:
Shot of lungs breathing (3D)
Camera swings up to show the 'sky' (3D)
Gets all moody and dramatic (2D)
Virus falls out of sky (2D)
Camera follows a single virus cell as it attaches to a cell (3D)
Virus attacks cell (2D)
Camera zooms out to reveal virus all over the place (3D) (or perhaps a mix of 3D and 2D)
So it will be a seamless transition rather than a big jump from 2D to 3D.