What is influenza (flu)?
Influenza (flu) is an easily spread respiratory tract infection. It is caused by a
virus. About 5% to 20% of people in the U.S. get the flu each year. The flu usually
starts abruptly, with fever, muscle aches, sore throat, and a cough.
The flu can make people of any age sick. Although most people are sick with the flu
for only a few days, some have a much more serious illness. They may need to go to
the hospital. The flu can also lead to pneumonia and death.
The flu viruses continually change. Currently, three different influenza viruses circulate
worldwide. Vaccines given each year to protect against the flu virus strain expected
to cause the illness that year.
What causes the flu?
The flu is caused by a virus. Viruses are generally passed from person to person through
the air when an infected person sneezes or coughs.
But the virus can also live for a short time on objects like doorknobs, pens, pencils,
keyboards, phones, and cups or eating utensils. So you can also get the flu by touching
something that has been recently handled by someone infected with the virus and then
touching your own mouth, nose, or eyes.
What are the symptoms of the flu?
Each person may experience symptoms differently. The flu is called a respiratory disease,
but it can affect your entire body. People usually become very sick with several,
or all, of the following symptoms:
- Cough, often becoming severe
- Extreme exhaustion
- Fatigue for several weeks
- High fever
- Runny or stuffy nose
- Severe aches and pains
- Sneezing at times
- Sometimes a sore throat
- Vomiting and diarrhea
Fever and body aches usually last for 3 to 5 days, but cough and fatigue may last
for 2 weeks or more.
The symptoms of the flu may look like other medical problems. Always talk your healthcare
provider for a diagnosis.
How is the flu diagnosed?
The flu is diagnosed based on your symptoms. Lab tests may be used to confirm the
diagnosis, if necessary.
How is the flu treated?
Specific treatment for the flu will be determined by your healthcare provider based
- Your age, overall health, and medical history
- Extent and type of flu, and severity of symptoms
- How long you’ve had symptoms
- Your tolerance for specific medicines, procedures, or therapies
- Expectations for the course of the disease
- Your opinion or preference
The goal of treatment for the flu is to help prevent or decrease the severity of symptoms.
Treatment may include:
- Antiviral medicines. They can reduce how long you’ll have the flu, but they can’t cure it. They have to
be started within the first 2 days of the illness. These medicines do have some side
effects, such as nervousness, lightheadedness, or nausea. These medicines are prescribed
by a doctor.
- Medicines. There are medicines for congestion and nasal discharge. You can also take medicine
to relieve aches and fever. Do not give aspirin to children with fever. The drug of
choice for children is acetaminophen.
- Rest. Bed rest and increased intake of fluids.
Talk with your healthcare provider for more information.
What are the complications of the flu?
The most common complication of the flu is pneumonia. It can also cause serious muscle
and central nervous system complications. Of those who get the flu, between 3,000
and 49,000 will die from it or from complications. Most of these deaths happen in
people ages 65 and older.
Can the flu be prevented?
A new flu vaccine is made each fall. Everyone ages 6 months and older should get a
flu shot each year. It is usually recommended for specific groups of people, as well
as for anyone who wants to avoid having the flu.
The flu shot is safe. The CDC and the FDA closely watch vaccine safety. Hundreds of
millions of flu vaccines have been safely given across the country for decades.
The flu shot can’t give you the flu. The most common side effects from a flu shot
- Low-grade fever
- Soreness where the shot was given
If you have them at all, these side effects are usually mild and last a short time.
The effectiveness of the vaccine varies from one person to another. It can depend
on factors such as age and overall health.
The following may also be helpful for preventing the flu:
- When possible, avoid or limit contact with sick people.
- Wash your hands frequently to reduce the risk of infection.
- Cover your nose and mouth when coughing or sneezing to limit spread of the virus.
The flu causes complications that may develop into a more serious disease or become
dangerous to some people. This includes older adults and those with chronic medical
problems. Always talk with your healthcare provider to find out if you should receive
the flu shot.
Although the flu shot is safe, some people should NOT be vaccinated. These include:
- People who are allergic to eggs
- People who have had a severe reaction in the past after getting the flu shot
- People who are sick with a fever (these people should get vaccinated after they have
- Babies who are age 6 months old or younger
- People who have a history of Guillain-Barré syndrome, a severe paralyzing illness,
after getting the flu shot
The CDC recommends getting the flu shot every year, as soon as it becomes available
in your community. Flu season can begin as early as October and most commonly peaks
in the U.S. in January or February, but flu seasons are unpredictable. The flu shot
takes 1 to 2 weeks to become effective.
The CDC recommends that travelers have the flu vaccine at least 2 weeks before planned
travel to allow time to develop immunity. Talk with your healthcare provider for more
When should I call my healthcare provider?
For most people, the flu can be treated at home without treatment from your healthcare
provider. However, if your condition or situation makes you more susceptible to complications
from the flu, tell your healthcare provider when you suspect you have the flu. If
your symptoms get worse or you have new symptoms, let your healthcare provider know.
Key points about the flu
- The flu is an easily spread viral respiratory tract infection.
- The flu is caused by viruses that are generally passed from person to person through
- The flu is treated with bedrest, increased fluid intake, and medicines to treat discomfort
- Antiviral medicines taken within the first 2 days of illness can reduce the length
and severity of the disease but does not cure it.
- Getting the flu shot every year is the best prevention.
Tips to help you get the most from a visit to your healthcare provider:
- Know the reason for your visit and what you want to happen.
- Before your visit, write down questions you want answered.
- Bring someone with you to help you ask questions and remember what your healthcare
provider tells you.
- At the visit, write down the name of a new diagnosis, and any new medicines, treatments,
or tests. Also write down any new instructions your provider gives you.
- Know why a new medicine or treatment is prescribed, and how it will help you. Also
know what the side effects are.
- Ask if your condition can be treated in other ways.
- Know why a test or procedure is recommended and what the results could mean.
- Know what to expect if you do not take the medicine or have the test or procedure.
- If you have a follow-up appointment, write down the date, time, and purpose for that
- Know how you can contact your healthcare provider if you have questions.