So you have a monster that can inflict an Injury Track disease. The PC successfully saves to avoid contracting the disease when he is injured in the first round of combat. If he is injured in the same way by the same creature in the 2nd round, does he need to save again or is he "immune" for the rest of the combat and/or day? I can't find where the RAW addresses this...
The rules are vague, but the best interpretation is that the character must save again if hit again in that combat.
The wording in the rules are a little vague on this point. The rule states:
Before an individual is subjected to an affliction, she is considered healthy in terms of the affliction’s progression track, if any. When initially targeted by an affliction, she must succeed at a saving throw to avoid its effects; if she fails, she is subject to the affliction.
The phrase "initially targeted" is the problem here. "Initially targeted" could be the first time in a combat, or a day, or their life... which would suggest that the character would then be immune for the rest of the combat, day, or their life. So what is the frame of reference? We must look at the context of the first sentence. The paragraph begins by establishing that characters begin at "Healthy" with respect to the affliction track, so that is the frame of reference for the second sentence. "Initially" refers to the course of the affliction track for an instance of exposure.
So a character is "healthy," they are initially targeted by the affliction and roll a saving throw. If they succeed in the saving throw, they remain healthy, the affliction track never begins, and the instance of exposure terminates. Everything resets for round two of the combat. The character is "healthy," they get hit again, they are initially targeted by the affliction again, and they must roll another saving throw. If they fail this time, they take the first step on the affliction track. Now they can no longer be "initially targeted" because they're afflicted and under way on the affliction track. The next time they must make a saving throw, they are being subsequently targeted by this instance of the disease. If they get cured, go on another adventure, and meet the same kind of monster and it hits them again, then they have been initially targeted by the disease again and must make a saving throw.