Influenza (flu)

Influenza (flu) is an infection in the lungs and breathing passages. It is caused by the influenza virus. There are different strains, or types, of the flu virus from year to year. Unlike the common cold, the flu comes on suddenly and the symptoms can be more severe. These symptoms include a cough, congestion, fever, chills, fatigue, aches, and pains. These symptoms may last up to 10 days. Although the flu can make you feel very sick, it usually doesn’t cause serious health problems.

Home treatment is usually all you need for flu symptoms. But your doctor may prescribe antiviral medicine to prevent other health problems, such as pneumonia, from developing. The risk of other health problems from the flu is highest for young children (under 2), older adults (over 65), pregnant women, and people with long-term health conditions.


What are the symptoms of influenza?

The symptoms of influenza appear suddenly. They often include: 

  • Fever of 100.4 F (38 C) to 104 F (40 C). 
    • Fever is usually continuous, but it may come and go. 
    • Fever may be lower in older adults than in children and younger adults. 
  • Body aches and muscle pain (often severe). 
  • A headache. 
  • Pain when you move your eyes. 
  • Fatigue, a general feeling of sickness, and loss of appetite. 
  • A dry cough, a runny nose, and a dry or sore throat. 

Symptoms usually are the worst for the first 3 or 4 days. But it can take 1 to 2 weeks to get completely better. 

It usually takes 1 to 4 days to get flu symptoms after you've been around someone with the virus. Some people can have the flu virus without having any symptoms. 

The flu usually doesn't cause symptoms in the stomach or intestines, such as vomiting and diarrhea. 


What causes influenza (flu)?

The flu is caused by the influenza virus. Common classes of the virus are type A and type B. Each type includes several subtypes or strains. Type A usually causes the yearly outbreaks that often occur in the late fall and early winter. 

The influenza virus changes often. So having the flu caused by one strain doesn't give you full immunity to other strains. 

The virus is spread from person to person through: 

  • Direct contact, such as shaking hands. 
  • Small droplets that form when a person sneezes or coughs. 
  • Contact with objects, such as handkerchiefs, that have touched fluids from an infected person's nose or throat. 

How can you prevent influenza (flu)?

You can help prevent the flu by getting the flu vaccine every year. It's best to get the vaccine as soon as it's available. The U.S. Centers for Disease Control and Prevention recommends that everyone 6 months old and older get a flu vaccine. 

You can also help avoid getting the flu by washing your hands often, keeping your hands away from your face, eating a balanced diet, exercising regularly and not smoking.