So many people think that a nasty, really bad cold is influenza. It is not, totally different, and anyone who has really experienced 'flu will confirm this. It used to be said that no matter how bad the cold, if you saw a £50 note flutter past your window, you would go to find this, with 'flu, there is no way you can even move from your bed.
Like many here, I began having my 'flu jabs when I was working at the local hospital and have continued every year since retirement.
It is, as has been said, a dead virus - however it takes between two to three weeks following the jab to be effective, so anything that your body is harbouring prior to the jab, or you are in contact with for several days afterwards, you will still get.
This year had mine end of September, no sore arm or any other effect. Had my pneumonia (once only) jab many years back and would love to have the shingles protective jab - but due to rather strange roll-out procedure I cannot get this until I am 78 years old in two years time.
The medics do try to forecast how the flu virus will change each year, but cannot ever be totally correct. However, some protection is surely better than none at all. Cannot understand anyone not taking advantage of this.