In the UK a flu shot isn't recommended for young healthy people at all, for "though [influenza] can be uncomfortable, [it] is not normally a serious disease"

From Boots (our main pharmacy chain) WebMD site:

"If you are under 65 years old and healthy, you won't need a flu jab as influenza, though it can be uncomfortable, is not normally a serious disease. An annual flu jab is recommended for certain high-risk individuals who are more prone to flu complications such as pneumonia.
People who should consider getting vaccinated each year are:
Pregnant women - pregnancy can increase your risk of flu complications such as pneumonia.
People 65 years or older
People who live in nursing homes
Anyone over six months of age with chronic heart or lung conditions, including asthma, a long-term kidney or liver disease, diabetes or with any condition that weakens the immune system
Anyone with lowered immunity due to disease or treatment (such as steroid medication or cancer treatment)
Any person in close contact with someone in a high-risk group, such as the main caregiver of an elderly or disabled person
a neurological condition eg. multiple sclerosis (MS) or cerebral palsy
a problem with your spleen, for example sickle cell disease, , or if you've had your spleen removed.
People who work in certain professions such as poultry workers"