I am certainly not an expert but I have a couple of questions Seasonal influenza is an acute respiratory infection caused by influenza viruses which circulate

I am certainly not an expert but I have a couple of questions Seasonal influenza is an acute respiratory infection caused by influenza viruses which circulate in all parts of the world. Did they just take the average of all these different viruses? Surely they don't all mutate at the same time. There is many times more instances of seasonal flu (currently) than covid. Surely the chance to mutate is per instance and therefore you need to take that into account when working out mutation rates. I don't see either of these points addressed in the article but again I'm not an expert so maybe there's good reason. If anyone could help with these questions I'd appreciate it greatly! Edit : typo