Here's Master Chief in quite a state, infected by the Flood! This custom started out from a McFarlane Master Chief 5" figure. Aves Studios Fixit Sculpt was used to sculpt the flood sections and I removed the mask lens, cracked it, and have the sensor tendrils coming out of there. The tendrils from the stomach (is that a mouth or its head?) are wires with the ends frayed and coated so they're bendy. His left hand was some sort of bone wing I modded to make the claw and you can see where it's busting out of the glove there and if you look close there's section of his black undersuit torn at the edges!
Sorry for deleting the first version of him. He broke in half when I was fiddiling with him, heh. Then I thought, yup, I could do more with him in two like this. So I added more stuff! Enjoy!
It was entirely possible for Chief to be a combat form. In the novelization of Combat Evolved, an infection form (running popcorn) had jabbed one of its claws into his neck but Cortana has fried it with his suit's electrical systems. The only question is, why didn't the lingering cells of the flood infect him into a minor form?
The flood infects it's victims by burrowing into them and attacking the nervous system. Thus, rearranging the structure of their bones and turning their organs into a slimy liquid. If they could not breach the host's skin then they'd simply die. And because spartan ll's are given near un-breakable skin and bones. They are unable to be converted into flood combat forms and will instead just simply die.
Everyone saying a Spartan can;t get infected is wrong. In Halo: The Flood an infection form cuts a hole in his jumpsuit near his neck but is killed when Cortana releases an electric shock from the suit. Also Grunts, Jackals, Buggers, and Hunters can't be infected and made into combat forms because of how weak they are however are made into Flood biomass and Carrier forms.