The influenza (flu) virus infects the nose, throat, and lungs, causing a contagious respiratory illness. Some people, such as the elderly, young children, and those with certain medical conditions, are more vulnerable to serious flu complications. Types A and B influenza viruses are the most common. Each year, seasonal flu epidemics are caused by the influenza A and B viruses that are routinely spread in humans. Most experts believe that flu viruses spread mainly by tiny droplets made when infected people cough, sneeze, or talk. These droplets can land in the mouths or noses of people who are nearby. Less often, a person might get flu by touching a surface or object that has the flu virus on it and then touching his or her own mouth, nose or possibly eyes.
Influenza can cause mild to severe illness, and at times can lead to death. Flu is different from a cold and usually comes on suddenly. People who have 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
CDC recommends a yearly flu vaccine as the first and most important step in protecting against flu viruses. Flu vaccines help to reduce the burden of flu illnesses, hospitalizations and deaths on the health care system each year. Vaccination of people at higher risk of developing serious flu complications is especially important to decrease their risk of severe flu illness.
Most people who get the flu recover in a few days to less than two weeks, but some develop complications like pneumonia as a result of the flu, some of which can be life-threatening and result in death.
Sinus and ear infections are examples of mild flu complications, whereas pneumonia is a serious flu complication that can result from flu virus alone or from flu virus and bacteria co-infection. Other serious complications caused by the flu include inflammation of the heart, brain, or muscle tissues, as well as multi-organ failure. A flu virus infection of the respiratory tract can cause a severe inflammatory response in the body, leading to sepsis, the body’s potentially fatal response to infection. Flu can also exacerbate chronic medical conditions. People with asthma, for example, may have asthma attacks while sick with the flu, and people with chronic heart disease may have their condition worsened as a result of the flu. Therefore, it is imperative to receive the flu vaccine every year to protect against the flu during flu season.