It hasn't really been mentioned, safe for the doctor's girlfriend, that they are in constant pain, that they actually struggle. We only hear about the superficial and tragic part of the phage but we forget that these guys are in constant pain, that some of them probably can't eat as they usually do, or they can't move in certain ways, or they get tired, or they sleep badly. They have probably lost their minds metaphorically in the quest for being more or less ok for a while, and they have also probably lost their minds literally in that the phage affects their brain too.

And we can assumen that the ones we see are actually some of the healthier ones, that the rotation in their army is frequent and fast, that they have excellent techonologies to keep organs alive and healthy for as long as possible, and excellent medical advances to make transplants work regardless of the combinations (or else this would be some Van Helsing's blood transfusion game of luck).

“Lifesigns” (S02E20, Stardate 49504.3) is the second episode this season to feature The Doctor heavily as he has an emotional crisis. This time he gets to experience love and the highs and lows it brings. Not as high-stakes as the earlier outing, but a quiet examination of what drives a human relationship.