Actually, those questions are the subject of a great deal of ongoing research. Given the high number of serious illnesses and deaths caused by the flu, there is a great deal of interest within the medical community in knowing those answers.
And, just like global warming, the answer will always be ‘needs more study!’. We will never know the answer though since they hide all the data AND the methods. Clever that. Very trustworthy.
You can guarantee there will NEVER be a government funded study that finds ANY vaccine is unnecessary. At least not while the treasury can pay for them. Your broken hip at age 70? good luck granny, hope they allow medical tourism!