Patient information from BMJ

Flu

Last published:Dec 14, 2023

Flu is caused by a virus. If you catch flu you'll probably feel very ill with a headache, fever, chills, and aches. But most people get better without needing any treatment. The virus can be spread from person to person by coughing, sneezing, talking, or touching surfaces that carry the virus and then touching your mouth, eyes or nose without washing your hands first.

What is flu?

Flu is an infection of your airways. It's caused by an influenza virus. The symptoms are similar to those of a cold, but just a lot more severe. Flu is most common in the late autumn, winter, and early spring.

What are the symptoms?

If you have flu you may get a fever (a high temperature 38°C or higher), chills, a dry cough, muscle aches, a headache, and a sore throat. You will probably also feel generally unwell and very tired.

Flu can make you feel terrible for a few days, but it isn't usually serious. But you should see a doctor if you get flu if and you are:

• Over 65 years old

• Pregnant, or

• You have a long-term medical condition, such as heart, lung, or kidney disease, or diabetes

• You have a weakened immune system (for example, if you are receiving medicine that affects your immune system, such as chemotherapy treatment for cancer, or if you have a condition like HIV.

You should also see a doctor if you feel very ill, have difficulty breathing, or are ill for more than 7 days. If you have young children and you are worried about their symptoms, you should take them to see a doctor.

What treatments work?

Most people with flu get better on their own. Usually the best thing to do is to stay at home, rest, and drink plenty of fluids. Paracetamol can help with aches or fever. Ibuprofen is another option.

Children can use versions of these medicines specially made for children. However, children under 16 should not take aspirin, as it can cause a rare but serious illness called Reye's syndrome, which leads to swelling in the liver and brain.

There are medicines to treat flu, called antiviral medicines. But most people don't need them. Doctors usually reserve them for people who are very ill, or who are more likely to become very ill from flu. These include older people, very young children, pregnant women, and people with a long-term medical condition that could make having flu more serious. 

Antiviral medicines work best if they are used within two days of the start of flu symptoms. People who take one of these medicines get better about a day or two sooner than people who don't take them. These medicines may also help prevent serious problems (complications), such as pneumonia. 

What will happen to me?

You'll probably feel pretty ill for about one week. And you may cough and feel tired for a couple of weeks. But most people recover from flu without any problems.

For some people, having flu is more serious. They may get problems such as bronchitis or pneumonia. This is more likely to happen if you're very young, older than 65, pregnant, or have another medical problem, such as a lung disease (for example, asthma) or heart disease.

Should I get a flu vaccine?

A flu vaccine won't help if you have flu. But it can reduce your chance of getting flu in the future. It's given as an injection or a nasal spray. To be protected you need to get a new flu vaccine each year, usually in the autumn.

Recommendations on who should get a flu vaccine vary from country to country. In some countries, such as the US, doctors advise people aged 6 months and older to get an annual flu vaccine.

In other countries doctors recommend that people have the vaccine if they have an increased chance of becoming seriously ill from flu. This may include people with long-term medical conditions, pregnant women, people aged 65 or older, and people living in a nursing home. If you are in close contact with someone who has an increased chance of becoing seriously ill from flu you may also be offered the vaccine. 

If you're allergic to eggs, talk to your doctor before getting the vaccine. Eggs are used to make some flu vaccines and you could have an allergic reaction. You should also tell your doctor if you've ever had a reaction to the flu vaccine before.

A flu vaccine can't give you flu. You might have a sore arm where the needle went in. You may also get muscle aches or a mild fever.