[Rebelgecko]

The 2021 flu shot was a different vaccine than the 2022 flu shot. Or to stretch the analogy, it's a different photo of a similar subject

[anon_coward_ghk]

Yes but the tetanus toxoid is the same toxoid it's always been. It is disingenuous to suggest that the immune system doesn't atrophy some with time. It's much more nuanced really, but humoral immunity in particular wanes with time.