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
Cough
Sore throat
Runny or stuffy nose
Muscle or body aches
Headaches
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.
Flu Complications
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 Severity
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 a regular flu season,
about 90 percent of deaths occur in people 65 years and older.
