Men’s immune systems weaken with increased testosterone - speculation is that this allows them to have less immune response so they can keep hunting and fighting.
Interesting; when my wife and I both get sick we always note this recurring theme where I get this intense but brief bout of illness, and her's are more drawn out and prolonged but significantly less intense. Timewise we're talking about 1-3 day sickness for me and 1-2wk sickness on her end. That recurring observation has caused a bunch of speculation between us about evolutionary protections and stuff where perhaps the man being down has more immediate risks that can threaten the family in the protecting role or something like that. Not sure entirely but fun to imagine about.
I thought the issue was the other way around in this case -- people were having bad results from COVID due to too severe of an immune response.
How does an immune response impact physical capability?
A fever is the result of an immune response.
Most of "feeling sick" isn't the actual bacteria/virus causing problems, it's your immune system doing things like raising your internal temperature to fight off the virus or generating boatloads of phlegm to do whatever that does.