Influenza (Flu)

What is Influenza (Flu)?

The flu is a contagious respiratory disease caused by influenza viruses that infect the nose, throat, and lungs. It can cause mild to severe illness, and at times can be fatal.

Anyone can get the flu as it is spread easily from person to person, usually when an infected individual coughs or sneezes.

Between 5 to 20 percent of people in the United States get the flu each year. Symptoms of the flu are similar to the common cold, but they last longer and tend to be worse.

Key Facts

  • Influenza is a highly contagious respiratory disease
  • Influenza is caused by one of three different viruses.
  • Most serious illnesses are caused by flu strains A and B.
  • Having lung diseases such as asthma puts you at higher risk of developing complications from the flu.
  • Getting you and your family vaccinated every year is the best protection from the flu.

Types of Influenza


Influenza Type A viruses can infect people as well as pigs, horses, birds, and other animals. Within the Influenza Type a virus, there are different strains which can infect humans. An example of such strains would be H1N1 and H3N2

Influenza Type B viruses can only be found in humans. While Influenza Type B viruses can cause illness among humans, it is generally associated with causing less severe infections than Influenza Type A.

Influenza Type C viruses cause mild illness in humans. Influenza Type C cases occur much less frequently than A and B and are typically not included in the seasonal flu vaccine.

How Influenza Affects Your Body

The flu affects your entire body including your nose, throat, and lungs. It can also lead to serious complications in individuals with chronic illness.

Complications can include pneumonia, ear or sinus infections, dehydration, and worsening of chronic medical conditions, such as congestive heart failure, asthma or diabetes.

Most people who have suffered from the flu before have described it like they have been hit by a truck. Flu symptoms, such as high fever, cough and muscle aches, usually come on suddenly and are more severe than colds.

How Serious Is Influenza?

A decrease in the quality of life, the impact of symptoms, the shifting nature of the virus, and the danger of life-threatening complications, combine to make the flu a major public health problem.

Every year there are about 3 to 5 million cases of severe illness and about 250,000 to 500,000 deaths due to influenza.