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Signs and Symptoms

For most people, the seasonal flu is a moderate illness that causes symptoms such as fatigue, fever, chills, stuffy nose, sore throat, headache, muscles aches, weakness, a cough and, with some strains, even diarrhoea and vomiting. These symptoms may also be seen with a variety of other conditions and seasonal viral infections.

Influenza can be severe and lead to complications such as viral pneumonia or secondary bacterial pneumonia (see Pneumonia) in the very young, the elderly, in those who are pregnant, and in those with underlying conditions such as asthmalung diseaseheart diseasediabeteskidney disease, liver disease, chronic neurological disease, and in those with compromised immune systems.

The incubation period for influenza is about two days. This is followed by several days of illness and then a resolution of symptoms. People shed virus and are infectious about a day before symptoms emerge and then for about five to seven days, or until about 24 hours after their fever ends.

Children and those with compromised immune systems may be infectious for longer periods of time.

What is the difference between influenza and the common cold?
While some bad colds can cause most of the symptoms above except diarrhoea and vomiting, in general, cold symptoms are milder than influenza. People with influenza generally have a moderate to high fever and muscle aches and pains. They feel very sick and need to stay in bed. Many people with a common cold are able to “soldier on” and continue daily activities even though they feel unwell. There are more than 100 viruses that can cause symptoms of the common cold, mostly rhinoviruses and coronaviruses. Because of this huge number of potential causes it is sometimes more difficult to identify the virus responsible for any particular common cold than it is to diagnose influenza.

Last Review Date: November 6, 2017