The flu jab is offered every year because seasonal influenza viruses can change, and the viruses circulating in one flu season may not be exactly the same as those in another.
Annual vaccination allows the seasonal flu programme to be updated according to the viruses expected to circulate.
Another reason is that protection from vaccination is seasonal rather than permanent.
The NHS therefore runs a seasonal flu vaccination programme each year for eligible groups.
For the 2026 to 2027 programme in England, eligibility includes groups such as people aged 65 and over, pregnant women, eligible children and people with certain long-term health conditions.
If you are unsure whether you should receive a Flu Jab UK, check the latest NHS guidance or discuss your circumstances with a healthcare professional.