I don't believe health is the problem of Deformed, it's just that they are easy to disable. In my opinion, a little speed boost and less or no speed penalty while burning would do.
Also, I've never seen people use Infected, I don't even know what model it is. It's a gimped version of Deformed offering no extras - trading off half the health for a little more speed and jump isn't really good enough. Infected should get something appealing, unique, not too overpowered.

On another note, human classes definately sounds fun.