The question requires a better understanding of the scenario. There are so many variations of the zombie sickness that knowing the type is important to this answer. Walking dead allows amputation as a means of quick save for a recent bite. I am not a fan of it personally, but I would definitely try it first. The next logical step would be to restrain the bitten comrade until the danger is clearly gone. I don't like this idea though. I think that if you are bit then the sickness is in your blood stream and through your body quicker than an amputation could be done. Hasty head shots on the other hand only make your group smaller and lower your chance of survival. People are resources too and they need to be salvaged whenever possible.