Compared to a common cold, the symptoms of flu are generally more severe and last longer. The fever also develops more suddenly and is usually higher than with a cold.
The most common symptoms of flu are:
- sudden high temperature of 38°C or above
- severe headache
- general aches, pains, tiredness and weakness
- shivering and chills
- aching muscles, pain in limbs or joints
- sore throat
- a runny or blocked nose, and sneezing
- a dry, chesty cough
- difficulty sleeping
However, sometimes flu can look like other types of illness, especially in children, so it can be hard to recognise:
- pain in the abdomen (stomach)
- loss of appetite
- nausea and vomiting
It is the complications of flu that are dangerous. The most common complication is a bacterial chest infection, which can develop into pneumonia. Other complications include:
- Middle ear infection (otitis media)
- Septic shock (a severe and life-threatening infection of the whole body)
- Meningitis (inflammation of the covering of the brain). See the Meningitis Research Foundation website for more detailed information on the signs and symptoms of meningitis.
- Encephalitis (inflammation of the brain)
Serious complications can affect anyone, even healthy people. They are more common in babies under six months, older people, those with certain long-term medical conditions, and pregnant women. During pregnancy, the baby may be affected, causing premature birth, low birth weight, or even death.
In the UK an average of 600 people a year die from complications of seasonal flu. However in 2013-14, it is estimated that about 11,000 people died from flu-related causes.