Right at the beginning of the film, when Jim woke up, what was the relevance him of being naked with no sheets? ITU doesn't nurse people naked, and who removed the sheets? There was no mention of why
I think it was done more to drive home the utter vulnerability of the character. What more of a vulnerable situation can you be in than to be naked in a hospital full of infected people who want to tear you apart. Or Perhaps he was in the middle of being sponge bathed when the hospital was overrun.
I think it was to liken man to the ape in the previous scene (more generally of course), shown in a similar position on the bed. The film has a lot of subtext about how animalistic humans can be. I think it says, "Humans are good enough test subject," or something of the sort.
At the very least I believe it connection human to our "more" animalistic apes in some way.
I thought that too - also the way he had a scar and shaved patch on his head made me think they were attempting to dissect him and experiment on him. I wish we got more information on that. I found it a little odd how he was even in a coma for so long in the first place, how his parents knew about it, how he had been hijacked and knocked out before even discovering the virus existed, etc... I guess it's more of a neat way to begin a story than anything else.
Maybe whoever was the last to see him (nurse or Dr) thought it was best that he not have anything on. Maybe they thought he might get tangled in the sheets or maybe as another poster said he was getting a sponge bath. I really don't think it was anything to do with symbolising man and ape or vulnerability... Whoever was there was obviously trying to help him as they locked him in so he'd be safe and they left the key.
It's suppose to represent Jim's rebirth into a new world he isn't familiar with. The Commentary track explains this.
I believe the main question being asked in this thread is what is the practical, real life context for him being naked rather than what it's suppose to symbolize.