Okay maybe I'm dumb but what is "con plague"? I've never heard the term and I've been to loads of cons. I'm assuming maybe something like the flu people catch at cons and stuff? I've never caught anything or been sick after any but I'd imagine following Covid type rules would work pretty well. Washing your hands constantly, avoid touching areas people touch a lot or wash your hands after you do, wear a mask or face covering, avoid the public bathrooms there, and avoid the most crowded areas. Make sure you don't sit anything like your cellphone or cups down on surfaces and wash them after the con.