I started off by looking at the microscopic view of the virus' that I am focusing my vehicles on. I took the basic shapes from these images and reproduce and repeated these shapes until I got 6/7 base outlines to work with. With these outlines I will pick 2 of each to develop, add more shapes to and add detail to.
The rabies virus to me looks like a rounded of bullet with spikes. With this in mind I mostly use circles, ovals and cylinders to come up with 7 basic shapes. I personally like 1,3,5. 1 because it is the one that looks the closest to the original virus. 3 as it has a bit more shapes to work with and 5 as I feel it has a good base shape to layer more detail and shape on top of it.
The Spanish flu (Influenza) microscopic virus is a basic shape, circle with cylinder spikes coming off it like the rabies virus. I looked at different interpretations of the virus and they were all based of circles, so with this I feel that the structure of this virus might have to be more visible to add more detail and character to this vehicle. I personally like 5 and 6. I like 5 because it already has a shape that stands out. I like number 6 as the multiple circles give more depth and range to the vehicle's shape.