Flu vaccination by injection, commonly known as the "flu jab", is available free every year on the NHS to protect people who are at higher risk of flu and its complications.
Flu can be unpleasant but, if you are otherwise healthy, it will usually clear up on its own within a week.
However, flu can be more severe in certain people, such as:
Anyone in these risk groups is more likely to develop potentially serious complications of flu, such as pneumonia (a lung infection), so it's recommended that they have a flu vaccine every year to protect them.
If you are in one of these groups, please take up the offer of free flu vaccination from your GP practice. It is available at some pharmacies too.
If you are not in an at-risk group, and you want to be immunised against flu, most pharmacies offer flu vaccination. There will be a charge.
Flu vaccine is the best protection we have against an unpredictable virus that can cause severe illness and death among at-risk groups, including older people, pregnant women and those with an underlying medical health condition.
Studies have shown that the flu jab does work and will help prevent you getting the flu. It won't stop all flu viruses and the level of protection may vary between people, so it's not a 100 per cent guarantee that you'll be flu-free, but if you do get flu after vaccination it's likely to be milder and shorter-lived than it would otherwise have been.
There is also evidence to suggest that the flu jab can reduce your risk of having a stroke.
Over time, protection from the injected flu vaccine gradually decreases and flu strains often change. So new flu vaccines are produced each year which is why people advised to have the flu jab need it every year too.
Read more about how the flu jab works.
Most adults can have the injected flu vaccine, but you should avoid it if you have had a serious allergic reaction to a flu jab in the past.
Read more about who shouldn't have the flu vaccine.
You can find out more by reading the answers to the most common questions that people have about the flu vaccine.
You can call 111 for advice if you need urgent medical help and are not sure what to do.
Call 111 when you need medical help fast but it's not a 999 emergency. NHS 111 is available 24 hours a day, 365 days a year. Calls are free from landlines and mobile phones.
If the illness or injury is life-threatening, don't hesitate. Call 999 straight away.