[Jim Noble]

Reduced effectiveness from annual flu vaccination (2015).

This has gotten quite a bit more complicated since this paper was published.

Immunity to influenza is dependent on age, age at first infection, strain of first infection, number of subsequent infections/types, number of subsequent influenza vaccinations - it may be literally true that, as regards effect of a single flu shot, "everybody's different".

[PeterPrinciple]

it may be literally true that, as regards effect of a single flu shot, “everybody’s different”.

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Yes, we are all unique. But our small minds can only hand two categories, it is good or it is bad.