Key Facts About the Flu
- Anyone can get the flu as it is spread easily from person to person, usually when an infected person coughs or sneezes.
- It's caused by one of three different viruses, although most serious illness is caused by flu strains A and B.
- If you have asthma or other lung diseases, you are at higher risk of developing complications from the flu.
- Getting vaccinated every year is the best way to protect yourself from the flu.
What Is Influenza (Flu)?
The flu is a contagious respiratory illness caused by flu viruses. The flu infects the nose, throat and sometimes the lungs. Each year, millions of people in the United States get sick with the flu. It can cause mild to severe illness, and in some cases, may lead to hospitalization or death.
Types of Influenza
There are three different influenza virus families that affect humans: A, B and C.
Influenza types A and B cause the most severe flu illness. The viruses change constantly and different strains circulate around the world every year. The body's natural defenses cannot keep up with these changes. Type C causes either a very mild illness or has no symptoms at all. It does not cause epidemics and does not have the severe public health impact that influenza types A and B do.
How Does the Flu Spread?
The flu mostly spreads through respiratory droplets that are made when people who are infected with the flu cough, sneeze or talk. The droplets pass through the air and enter the body of people nearby through their mouth or nose. The virus can also infect a person if they touch a surface with the virus on it and then touch their mouth, nose or eyes.
Understanding Respiratory Viruses
Learn how respiratory viruses spread, infect the airways and trigger the body's immune response. This video explains the basic processes behind respiratory infections, including influenza (flu).
How Serious Is the Flu?
Seasonal flu causes millions of illnesses, hundreds of thousands of hospitalizations, and tens of thousands of deaths every year in the United States. Although most people recover within a week or two after having the flu, certain people are at increased risk of developing severe complications. If you are living with asthma, chronic obstructive pulmonary disease (COPD) or other underlying medical conditions you are at higher risk of developing complications from the flu. Complications can include pneumonia, ear or sinus infections, dehydration, and worsening of chronic medical conditions.
Prevent the Flu: Get Vaccinated
Everyone 6 months of age and older should get a flu vaccination every year. Most likely, this includes you and your entire family. Speak with your healthcare provider to learn more about receiving an annual flu vaccination. Find a flu vaccine provider near you.
Infectious Respiratory Disease Basics
Learn about infectious respiratory diseases, prevention strategies, vaccination information and treatment options through this free, self-paced interactive module.
Page last updated: November 11, 2026
