Flu (Influenza)

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What Is Flu?

Influenza, commonly called flu, is a disease caused by a group of viruses that infect the nose, throat, and lungs. Many people have mild symptoms and recover in a few days to two weeks, but flu can be serious or even fatal. Even healthy children and adults can get very sick from flu. Getting an annual flu vaccine is the best way to prevent flu and protect against serious flu illness.

A Quick Guide to Flu

How it spreads	Droplets released when infected people cough, sneeze, or talk Touching contaminated surfaces, then touching your eyes, nose, or mouth A person can spread flu to others even before they know they are sick
Common symptoms	Think F.A.C.T.S.: Fever Aches (muscle, body, and headaches) Chills Tiredness (fatigue) Sudden onset
Impact	While the numbers vary, each year in the US: Millions of people get sick from flu Hundreds of thousands are hospitalized Tens of thousands die from flu and related complications
Vaccine?	Yes
Can it be cured?	No, but it can be treated

How Common or Serious is Flu?

Millions of people get flu every year in the US, though some years are worse than others. Many people recover from flu within a few days to two weeks. However, flu can cause serious complications or even death. Each year in the United States, millions of people get sick from flu, hundreds of thousands are hospitalized, and tens of thousands die from flu and related complications.

According to preliminary estimates for the 2025-2026 flu season from the US Centers for Disease Control and Prevention(opens in new tab) (CDC), there have been at least 32 million illnesses, 390,000 hospitalizations, and 24,000 deaths from flu, including 192 deaths in US children.

Flu can weaken the immune system and lead to other infections, including:

• lung infections (pneumonia)
• ear infections
• sinus infections

Flu can also cause other problems, such as:

• heart damage
• muscle swelling
• brain or nerve damage

Flu can worsen medical problems that people already have.

Flu does not just affect health. According to a study(opens in new tab) by the Global Healthy Living Foundation(opens in new tab) and Adult Vaccine Access Coalition(opens in new tab), the 2023–2024 flu season cost the United States nearly $29 billion in medical expenses and lost productivity.

What Causes Flu?

Influenza viruses cause flu. They spread:

• in droplets when an infected person coughs, sneezes, or talks
• when a person touches something that has the virus on it and then touches their eyes, mouth, or nose

A person can spread flu to others even before they know they are sick and for a week or more after they start to feel sick. People with flu are usually most contagious during the first 3 days of illness.

Who Is at Risk for Flu Complications?

Anyone can get seriously ill from flu, but young children, older adults, pregnant women, and people with certain health conditions face a greater risk of complications.

These factors raise the chances of serious complications:

• age 2 or younger
• age 65 or older
• pregnancy
• asthma
• diabetes
• obesity
• heart, lung, liver, or kidney disease
• stroke or other blood vessel disease
• sickle cell disease or other blood conditions
• conditions that make it hard to cough or swallow
• weakened immune system from treatment for cancer, HIV/AIDS, or other causes

What Are the Symptoms of Flu?

Flu is not just a common cold. It usually comes on suddenly, and people with flu may have some or all of the following symptoms (think F.A.C.T.S.):

• Fever
• Aches (muscle, body, and headaches)
• Chills
• Tiredness (fatigue)
• Sudden onset
• Cough, runny or stuffy nose, and/or sore throat
• Vomiting and diarrhea (more common in children than adults)

Flu often shares many symptoms with the common cold, COVID-19, and respiratory syncytial virus (RSV), including a fever, stuffy or runny nose, coughing, and sneezing. To help you tell the difference, the National Foundation for Infectious Diseases (NFID) developed a simple chart, available in English and Spanish(opens in new tab).

Most symptoms can be handled at home, but people with any of these symptoms should get emergency medical help immediately:

• Trouble breathing
• Bluish skin
• Chest pain
• Confusion
• Trouble waking up or staying awake

How Can You Prevent Flu?

The best way to prevent flu and protect against serious illness is to get a flu vaccine every year.

Annual flu vaccination is recommended for everyone age 6 months and older. The best time to get vaccinated is in the fall, before influenza viruses start spreading in your community, but getting vaccinated any time throughout the season is still beneficial.

Flu vaccines are updated each year to protect against the influenza viruses expected to spread during the upcoming season. Flu vaccines can vary in how well they work, but even when flu vaccination does not prevent infection completely, it can make the illness milder and prevent serious complications.

For more than 50 years, hundreds of millions of people in the US have safely received seasonal flu vaccines.

Several forms of vaccine are available, including:

• Nasal spray for healthy people age 2-49 who are not pregnant or immunocompromised
• High-dose vaccines for adults age 65 years and older

View immunization recommendations from the American Academy of Family Physicians, American Academy of Pediatrics, American College of Obstetricians and Gynecologists, and Infectious Diseases Society of America (opens in new tab)

View CDC Interim Clinical Considerations for the Use of Seasonal Influenza Vaccines in the United States(opens in new tab)

Other steps to lower your chances of getting sick or spreading flu include:

• Wash hands with soap and water for at least 20 seconds or use hand sanitizer
• Cover coughs and sneezes with a tissue
• Avoid close contact with people who are sick
• If you feel sick, stay home to avoid spreading disease to others.

How Is Flu Treated?

Antiviral drugs can reduce symptoms and shorten the time you are sick. They also can lower the chances of serious complications. They need to be taken quickly, however. Antivirals work best when given in the first two days after symptoms start, but they can still help if taken later. Healthcare professionals may treat patients based on clinical judgment, local flu activity, and patient conditions.

CDC recommends that anyone who is hospitalized, severely ill, or at high risk for developing serious flu-related complications should be treated with antiviral drugs immediately if flu is suspected.

Most people who aren’t at risk of complications won’t need antivirals. Rest, fluids and over-the-counter drugs will manage the symptoms.

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Updated and Reviewed September 2026

Sources: American Academy of Family Physicians, American Academy of Pediatrics, American College of Obstetricians and Gynecologists, Centers for Disease Control and Prevention, and the Infectious Diseases Society of America