Flu vaccination is available every year on the NHS to help protect adults and children at risk of flu and its complications. Flu can be unpleasant, but if you're otherwise healthy, it'll usually clear up on its own within a week.
But flu can be more severe in certain people, such as: Anyone aged 65 and over, pregnant women, children and adults with an underlying health condition (such as long-term heart or respiratory disease) or with weakened immune systems.
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 help protect them.
Flu vaccine is the best protection we have against an unpredictable virus that can cause unpleasant illness in children and severe illness and death among at-risk groups, including older people, pregnant women and those with an underlying medical health condition.
Serious side effects of the injected flu vaccine are very rare.
You may have a mild fever and aching muscles for a couple of days after having the vaccine, and your arm may be a bit sore where you were injected.
Side effects of the nasal spray vaccine may commonly include a runny or blocked nose, a headache, tiredness and some loss of appetite.
The flu vaccines used in the national programme have a good safety record.
Flu vaccines that have been licensed recently in England have been thoroughly tested before they're made available, and have been used in other countries with a good safety record.
The best time to have a flu vaccine is in the autumn, from the beginning of October to the end of November.
But do not worry if you have missed it, as you can have the vaccine later in winter. Ask a GP or pharmacist.
Most adults can have the injected flu vaccine, but you should avoid it if you have had a serious allergic reaction to a flu vaccine in the past.
You can find out more by reading the answers to the most common questions that people have about the flu vaccine.