I've heard this even from people who work in the field that some years they work great and some years, they don't work at all.
The reason being is that they're basically trying to figure out how the common strains are mutating before they even become prevalent. Sometimes they get it right, sometimes they miss.
I get them most every year cause of my heart, (actually missed a few cause I was starting to wonder about their effectiveness) and I can say that seems right to me. Sometimes it really seems to make a difference, and other years, not so much.
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