It's actually quite insane that this dude is basically an athlete (has videos about how to work out in adverse frontline conditions etc.) and infantry soldier with such levels of debilitating allergies. Basically what's happening to him that being allergic, all sorts of contaminants/pollutants will trigger a highly inflammatory reaction in his lungs and airways, and that inflammation will also make him more vulnerable to catching whatever bugs are doing the rounds, so after some asthmatic crisis he'd probably get an infection too, and then comes the pneumonia.
Super nasty shit. I know people that are literally wearing N95s during spring time, pollen etc. Some even in their homes if they cannot avoid their allergens.
Since he received injectable corticosteroids, I assume the inflammation was so bad that they couldn't fix it with anything else. That comes with its own set of adverse effects and issues.
I'm surprised he is not getting the same allergies though in the US. Must be some flora that's specific to Ukraine.
Still, crazy that he works out and keeps fit. Most people with such issues are nearly fully wrecked.