Search Menu
Search entire library by keyword
Choose by letter to browse topics
A B C D E F G H I J K LM N O P Q R S T U V W X Y Z 0-9
(A-Z listing includes diseases, conditions, tests and procedures)

Influenza (Flu)

Flu: What You Need to Know

  • The flu is an easily spread respiratory tract infection caused by a virus.

  • Most people are sick with the flu for only a few days, but young children, the elderly and those with impaired immune systems may develop a much more serious illness.

  • Flu viruses continually change. Vaccines given each year fight the strain predicted to cause illness that year.

  • Flu season can begin as early as October and most commonly peaks in the U.S. in January or February.

  • The flu shot is one of the best — and easiest — ways to keep you and your family healthy.

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, telephone receivers and eating utensils. You can get the flu by touching something that has been recently handled by someone who has the virus and then touching your own mouth, nose or eyes.

More Information About the Flu from Johns Hopkins Medicine

Woman sneezing with the flu

Ask the Expert

Each year, between 5 to 20 percent of Americans get the flu, sending many to the hospital with severe complications. Learn how you and your loved ones can stay healthy with answers from internal medicine physician Michael Albert.

Read more.

What are the symptoms of the flu?

Each person may experience symptoms differently, but people usually become very ill with several, or all, of the following symptoms:

  • High fever

  • Headache

  • Runny or stuffy nose

  • Sneezing

  • Cough, which often becomes severe

  • Severe aches and pains

  • Extreme exhaustion

  • Sore throat (less common)

Fever and body aches usually last for three to five days, but cough and fatigue may last for two weeks or more.

The symptoms of the flu may look like other medical conditions. Always consult your health care provider for a diagnosis.

What should I do if I suspect my child has the flu?

Worried that your child caught the flu? Johns Hopkins epidemiologist Aaron Milstone details the steps you should take to restore your child back to full health — and shares when they’re ready to go back to school.

How is the flu diagnosed?

Your doctor will diagnose you 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 health care provider based on:

  • Your age, overall health and medical history

  • Extent and type of influenza and severity of symptoms

  • How long you’ve had symptoms

  • Your tolerance for specific medications, 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:

  • Medications to relieve aches and fever. Do not give aspirin to children with fever. The drug of choice for children is acetaminophen.

  • Medications for congestion and nasal discharge

  • Bed rest and increased intake of fluids

  • Antiviral medications. When started within the first two days of the illness, they can reduce how long you’ll have the flu, but they can’t cure it. These medications do have some side effects, such as nervousness, lightheadedness or nausea. These medications are prescribed by a doctor

More Information About Flu from Johns Hopkins Medicine

Anesthesia May Help with Flu Treatment Shortages

Inhaled anesthetics have made modern surgery possible. Now, researchers at Johns Hopkins and elsewhere have added to evidence that certain anesthetics — routinely used during surgeries — may also possess powerful effects on the immune system that can combat viral and bacterial infections in the lung, including influenza and pneumonia.

Read more.

Can the flu be prevented?

The best way to prevent the flu is to get a flu shot each year.

  • Everyone 6 months and older should get a vaccine each flu season.

  • The flu vaccine is safe. The Centers for Disease Control and Prevention and the Food and Drug Administration closely watch vaccine safety, and hundreds of millions of flu vaccines have been safely given across the country for decades.

  • The flu vaccine can’t give you the flu. The most common side effects from a flu shot are soreness where the shot was given and maybe a low fever or achiness. The nasal spray flu vaccine might cause congestion, runny nose, sore throat or cough. If you do have them at all, these side effects are usually mild and short-lived.

Young children, older adults and those with chronic medical conditions are most at risk of serious complications. It’s especially important for these groups to get a vaccine each year:

  • People 50 and older

  • Children and teens 6 months to 19 years old

  • Residents and employees of nursing homes and any other care facilities that house people of any age who have chronic medical conditions

  • Adults and children who have chronic disorders of the lungs or heart, including children with asthma

  • Adults and children who have these medical conditions:

    • Chronic metabolic diseases, such as diabetes

    • Kidney dysfunction

    • Compromised immune system, e.g., from HIV/AIDS or treatment for certain diseases, like cancer

    • Blood disorders, such as sickle cell disease

  • Children and teens ages 6 months to 19 years old who take aspirin as long-term therapy

  • Women who will become pregnant during flu season

  • Health care providers

  • Providers of home care to people at high risk

  • Household members, including children, of high-risk groups

Although the flu immunization is safe, some people should not be vaccinated. These include:

  • People who are sick with a fever — these people should get vaccinated after they have recovered

  • Babies who are 6 months or younger 

  • People who have had a severe reaction in the past after getting the flu vaccination

  • People who have a history of Guillain-Barré syndrome, a severe, paralyzing illness, after getting a prior flu shot

Nasal Spray Vaccine

A nasal spray flu vaccine is currently approved to prevent flu in healthy children and teens ages 2 to 17 and healthy adults ages 18 to 49. As with other live virus vaccines, the nasal spray vaccine should not be given to pregnant women or people with weak immune systems. This includes those with immune deficiency diseases, such as HIV/AIDS or cancer, or people who are being treated with medications that weaken the immune system. The nasal spray vaccine also should not be given to these groups of people:

  • Children younger than 2

  • Any person with asthma

  • Children younger than 5 who have wheezing

  • Adults 50 and older

  • Children and adolescents who take aspirin as long-term treatment

  • Children and adults who have a chronic disorder of the lung, heart, kidney, liver, nerves, blood or metabolism

What are the complications of the flu?

The most common complication of the flu is pneumonia. The flu 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 occur in people over 65.

When should I call my health care provider?

For most people, the flu can be treated at home without treatment from your health care provider. However, if your condition or situation makes you more susceptible to complications from the flu, tell your health care provider when you suspect you have the flu. If your symptoms get worse or you have new symptoms, let your health care provider know.

When should I seek medical care for my child?

Think it’s time to see a doc? Johns Hopkins epidemiologist Aaron Milstone outlines the symptoms parents should look for that indicate serious illness.

Experience Our Care

Find a physician at another Johns Hopkins Member Hospital:
Connect with a Treatment Center:
Find Additional Treatment Centers at: