Influenza (also known as the flu) is a contagious respiratory illness caused by flu viruses. It can cause mild to severe illness, and at times can lead to death. The flu is different from a cold. The flu usually comes on suddenly. People who have the flu often feel some or all of these symptoms:
- Fever* or feeling feverish/chills
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Fatigue (tiredness)
- Some people may have vomiting and diarrhea, though this is more common in children than adults.
* It’s important to note that not everyone with flu will have a fever.
Most people who get influenza will recover in a few days to less than two weeks, but some people will develop complications (such as pneumonia) as a result of the flu, some of which can be life-threatening and result in death.
Pneumonia, bronchitis, sinus and ear infections are examples of complications from flu. The flu can make chronic health problems worse. For example, people with asthma may experience asthma attacks while they have the flu, and people with chronic congestive heart failure may experience worsening of this condition that is triggered by the flu.
People at High Risk from Flu
Anyone can get the flu (even healthy people), and serious problems related to the flu can happen at any age, but some people are at high risk of developing serious flu-related complications if they get sick. This includes people 65 years and older, people of any age with certain chronic medical conditions (such as asthma, diabetes, or heart disease), pregnant women, and young children.
Flu is unpredictable and how severe it is can vary widely from one season to the next depending on many things, including:
- what flu viruses are spreading,
- how much flu vaccine is available,
- when vaccine is available,
- how many people get vaccinated, and
- how well the flu vaccine is matched to flu viruses that are causing illness.
Over a period of 30 years between 1976 and 2006, estimates of flu-associated deaths in the United States range from a low of about 3,000 to a high of about 49,000 people. During recent flu seasons, between 80% and 90% of flu related deaths have occurred in people 65 years and older.