My SO has begun immunosuppressive therapy

Hello everyone, this is my first post after a bit of lurking in the forum. I need to talk to someone who has already lived this experience, because not having anyone around to talk to is really powering up my anxiety. My SO has had psoriasis for 15 years, but lives the condition fairly well, with no comorbidities or side effects aside from the occasional unreachable itch, for which I have honed my back-scratching game. Giving in to his father's insistence, he has recently begun immunosuppressive therapy with Skilarence. We've made some research and found it that, while effective, it's quite a powerful drug, and that the side effects can be pretty nasty. After coming to the realization that an immunosuppressant actually suppresses the body's immune system (duh!) I have grown very anxious about my SO contracting some illness he wouldn't be able to fight off with a weakened immune system. I am terrified to be the one to bring something bad home, as I work on crowded passenger trains, and my employer isn't exactly famous for taking precautions to protect their employees, not even during a pandemic. As we talk about this with his father, and we mention the fact that my SO was pressured into the treatment without really being told what it was, we get told that we're overreacting, that he just has to take his pills, feel like shit for a while, man up, go for a run and think positive, then, one day -bam!- psoriasis no more. My SO, being the sweet and nonconfrontational individual he is, is gritting his teeth and trudging through the treatment, but he's told me he doesn't like it and would prefer interrupting it, especially because he's never experienced any of the problems that the therapy should treat. I can see he's sad and afraid. I don't know what to advise him. I am angry with his father for pressuring him and for oversimplifying the whole thing. I am anxious about the drug's side effects, about the fact that he's getting immunosuppressive therapy during a pandemic all willy-nilly, about how distressed he will feel. I don't want to see him suffer, especially for treating something that didn't cause any distress in the first place. I can't think of anything else, but we have no one close to us that understands the situation. I'm bottling it all up, as I don't want to stress my SO any more. I don't even know what kind of answers I really expect to this long and ranty mess, I guess I just really needed to vent. Thanks for reading through my wall of text, and have a pleasant evening everyone.