Complications of flu mostly affect people in high-risk groups, such as the elderly, pregnant women and those who have a long-term medical condition or weakened immune system.
This is why it's important for people in these groups to have the annual flu vaccination and consider seeing their GP if they develop symptoms of flu.
The most common complication of flu is a bacterial chest infection, such as bronchitis. Occasionally, this can become serious and develop into pneumonia.
A course of antibiotics usually cures a chest infection or pneumonia, but it can very occasionally become life-threatening, particularly in the frail and elderly.
Worsening of existing conditions
In some people with long-term health conditions, getting flu can make their condition worse.
For example, people with lung conditions such as asthma or chronic obstructive pulmonary disease (COPD) may find that their symptoms become more severe when they get the flu.
In people with diabetes, flu can affect blood sugar levels, potentially causing hyperglycaemia (high blood sugar) or, in people with type 1 diabetes, diabetic ketoacidosis (a dangerous condition caused by a lack of insulin in the body).
If you have type 1 diabetes or have type 2 diabetes and take insulin, it's a good idea to monitor your blood sugar level more closely while you’re feeling unwell.
If you get flu while you're pregnant, there's a risk that the infection could cause problems with your pregnancy.
Flu may cause you to go into premature labour (before 37 weeks of pregnancy), or it may result in your baby having a low birth weight.
Occasionally, getting flu during pregnancy can result in a miscarriage or stillbirth.
Less common complications of flu include:
Click on the links above for more information about the symptoms of these conditions and to find out how they're treated.