[KenBo]

I would say it is because there are many different types of flu.
The medics produce a vaccine based upon historical results, if a different strain then comes along then the success of that particular vaccine is hindered.
Just my thoughts without any medical background lol.

[Tosh Crabtree]

I had flu jabs fairly regularly most years , until 3 years ago .
After having that one in 2017 , I spent 4 days in bed .
It was a feeling far worse than the flu itself.
I honestly thought I was dying .
I've never taken the chance of having a flu jab since .
And , touch wood , I haven't had flu .

[Tosh Crabtree]

Thesedays, I try and stay away from all forms of medication , if possible.
Some alternative remedies are more successful , without the risk .