In the paper you link the suggested mechanism for vaccine fatigue is the immune system under-reacting to the new vaccine, because because it's too similar to th

In the paper you link the suggested mechanism for vaccine fatigue is the immune system under-reacting to the new vaccine, because because it's too similar to the old vaccine. The effect vanes over time, and most certainly is not relevant to tetanus. [...] This hypothesis holds that the impact on the current season’s vaccine effectiveness is most pronounced when the difference between last season’s vaccine component and the current season’s vaccine component is small (this year they’re identical). In that case, the current season’s vaccine may boost memory of the earlier vaccine’s antibody responses; then these “old” antibodies may mop up the current vaccine’s antigen before the newly vaccinated person can mount an immune response to it (this is called antibody interference). [...]