Fr said:
anc[is]Short version: She's alien, it works differently for her
I forget the exact reasoning, but the Quarians and Turians are different in that regard. It's like they have a different OS. A human disease can interact with the human OS and cause trouble. The quarian OS wouldn't be able to read it, and the disease couldn't do anything either. So perhaps the quarians have bad antivirus software, but their "idk wtf this is" response might be way too strong.
Yes, I'm aware of this. I even mentioned it above (why quarians can't catch any human disease). So yes, it makes sense that they'd want to fix that logical error.
My issue is that they only half-fixed it. Half the time, Tali says what you said above. That's an allergic reaction - the body's system over reacting to something that can't harm it. But, she also talks about "weak immune systems" and "taking immune boosters" to leave her suit. A weak immune system can't have an allergic reaction, and immune boosters make allergic reactions worse.
How do I know? Because we have those and do that today. Again, tell me that aliens have a different type of DNA, I'm cool with that. Tell me that immune boosters will help an allergy and I cry foul the same way I would if you told me that I could freeze something by increasing its temperature. They are opposite terms - one cannot cause the other.