What is influenza (flu)?

Influenza (flu) is a viral infection. People often use the term "flu" to describe any kind of mild illness, such as a cold or a stomach virus, that has symptoms like the flu. But the real flu is different. Flu symptoms are usually worse than a cold and last longer. The flu usually does not cause vomiting or diarrhea.

Most flu outbreaks happen in late fall and winter.

What causes the flu?

The flu is caused by influenza viruses A and B. There are different strains, or types, of the flu virus every year.

What are the symptoms?

The flu causes a fever, body aches, a headache, a dry cough, and a sore or dry throat. You will probably feel tired and less hungry than usual. The 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 symptoms of the flu after you have been around someone who has the virus.

Most people get better without problems. But sometimes the flu can lead to a bacterial infection, such as an ear infection, a sinus infection, or bronchitis. In rare cases, the flu may cause a more serious problem, such as pneumonia.

Certain people are at higher risk of problems from the flu. They include young children, pregnant women, older adults, and people with long-term illnesses or with impaired immune systems that make it hard to fight infection.

How is the flu diagnosed?

Your doctor will ask you about your symptoms and examine you. This usually gives the doctor enough information to find out if you have the flu, especially if many cases of a similar illness have occurred in the area and the local health department reports a flu outbreak.
In some cases, the doctor may do a blood test or take a sample of fluid from your nose or throat to find out what type of flu virus you have.
How is it treated?

Most people can treat flu symptoms at home. Home treatment includes resting, drinking plenty of fluids, and taking medicine to lower your fever.
If you think you have the flu, your doctor may be able to give you medicine that can make the symptoms milder. But you need to start taking it within 2 days of your first symptoms.

Can the flu be prevented?

You can help prevent the flu by getting the flu vaccine every year. The best time to get the vaccine is in October or November, just before the start of flu season. You can get the vaccine as a shot or in a spray that you breathe in through your nose.

Almost anyone over 6 months old can have the flu vaccine. The vaccine is especially important for people who are at higher risk of problems from the flu, including:1
Children between 6 months and 5 years of age.

Adults age 50 and older.

Adults and children who have long-term health problems or an impaired immune system.
Women who will be pregnant during the flu season.

The flu vaccine is also recommended for health care workers and anyone who lives or works with a person who is at higher risk of problems from the flu. Your doctor can help you decide if the flu vaccine is a good choice for you.

The vaccine prevents most cases of the flu. But even if you do get the flu after you've had the vaccine, your symptoms will be milder and you'll have less chance of problems from the flu. You cannot get the flu from the flu vaccine.