Sure, but EU countries are now discussing limiting the duration of the covid passport to 9 months already. That would mean, at a minimum, an extra shot every 9 months.

Thing is there are many 'colds' and 'flus' and the chance the catch a specific one may isn't that likely depending on where and how you live.

Does that change anything? Covid is as contagious as any of them and all of them and immunity people gain against covid dimnishes in the matter of months. After few years it may drop to near zero as it is in the case of some other cold viruses.