Influenza (flu)

Overview

Influenza, or the flu, is an illness caused by flu viruses. It infects your nose, throat, and sometimes your lungs. It spreads easily from person to person, mostly in the fall and winter.

The flu can feel like a bad cold, but it usually comes on suddenly and makes you feel much sicker. Most people get better at home. Some people get very sick, especially young children, adults 65 and older, pregnant people, and people with health problems like asthma, diabetes, or heart disease.

"Stomach flu" is a different illness. It's caused by other viruses, and the flu vaccine doesn't protect against it.

Symptoms

Flu symptoms usually start suddenly, about 2 days after you catch the virus (anywhere from 1 to 4 days).

• Fever or feeling feverish, with chills (not everyone has a fever)
• Muscle or body aches
• Feeling very tired (fatigue)
• Cough
• Headache
• Sore throat
• Runny or stuffy nose

Less common

• Vomiting and diarrhea, more often in children
• Chest discomfort

How it usually goes

• Days 1–3: Symptoms hit hard: fever, aches, and tiredness. You're most contagious now. Flu medicine works best if started in these first 2 days.
• Days 4–7: Fever usually goes away and you start to feel better. A cough and tiredness often hang on.
• Week 2: Most people are close to normal. Tiredness and a cough can last a little longer.

Look up a symptom: Body aches · Chills · Cough · Fatigue · Feeling weak all over · Fever · Headache · Runny nose · Sore throat

When to get medical care

Causes

The flu is caused by influenza viruses. Types A and B cause the yearly flu season. The viruses change a little every year, which is why you can get the flu again and why the vaccine is updated each year.

The flu spreads mainly through tiny drops when people with the flu cough, sneeze, or talk. Less often, you can catch it by touching a surface with the virus on it and then touching your mouth, nose, or eyes. You can spread the flu starting 1 day before symptoms start and for 5 to 7 days after getting sick. Young children and people with a weak immune system may spread it longer.

Does it spread or run in families?

• Yes, it can spread from person to person.
• How it spreads: coughs or sneezes.
• Washing hands often and staying home when sick help protect others.

Who is more likely to get it

• Adults 65 and older, who are more likely to have serious problems
• Children under 5, especially under 2
• Pregnant people, and people who gave birth in the last 2 weeks
• People with long-term conditions, like asthma, diabetes, heart disease, kidney disease, or a weak immune system
• People who live in nursing homes or other long-term care homes

Possible complications

• Pneumonia: A lung infection from the flu itself or from bacteria; the most serious common problem
• Ear infection: Ear pain or fever, most often in children
• Sinus infection: Face pain and congestion
• Asthma flare: Wheezing or trouble breathing
• Heart inflammation: Rare; chest pain or a racing heartbeat
• Sepsis: Rare; the body's extreme reaction to an infection

Diagnosis

Many people with the flu don't need to see anyone and can get better at home. If you do see a healthcare professional, they can often tell it's the flu from your symptoms, especially when the flu is going around. If you're at higher risk, they may start flu medicine without waiting for a test.

Questions you may be asked

• When your symptoms started, and whether they came on suddenly
• Your highest temperature
• Whether anyone around you has the flu
• Whether you got a flu vaccine this season
• Whether you're pregnant or have asthma, diabetes, heart disease, or another long-term condition

The exam

They'll usually check your temperature, look in your throat and ears, and listen to your lungs. If you're short of breath, they may check your oxygen level with a small clip on your finger.

Tests

A test isn't always needed. Your healthcare professional may test you if it would change your care:

• Flu test: A swab of the nose or throat. Some results are ready in 15 to 20 minutes. A negative quick test doesn't always rule out the flu.
• Flu and COVID-19 test: One swab can check for both, since they cause similar symptoms but have different medicines.
• Chest X-ray: If pneumonia is a concern because of trouble breathing or a cough that gets worse.

Treatment

Most people with the flu get better at home with rest and fluids. Antibiotics don't work on flu viruses. Prescription flu medicines (antivirals) can make the flu shorter and milder, and they work best when started within 2 days of the first symptoms.

Self-care

• Stay home and rest except to get medical care
• Drink plenty of fluids like water, broth, and warm drinks
• Treat fever and aches with acetaminophen or ibuprofen at the right ages (see Medicines)
• Cover coughs and sneezes and wash your hands often to protect others
• Go back to your normal activities only after at least 24 hours of feeling better overall and having no fever without fever medicine

Medicines

Prescription flu medicines fight the virus. Over-the-counter medicines can ease fever and aches but don't make the flu go away faster. Read labels, and ask a pharmacist if you take other medicines.

Medicine names link to drug information from the U.S. National Library of Medicine (MedlinePlus). OwieClear doesn't give doses: follow the label or your healthcare professional.

Call a healthcare professional right away if you're at higher risk, very sick, or worried. They may prescribe a flu medicine. It's most helpful in the first 2 days, but it can still help later for people who are very sick or at high risk. If the flu leads to a bacterial infection, like pneumonia or an ear infection, you may need an antibiotic for that infection.

How it compares

Prevention

A yearly flu vaccine is the best way to protect yourself. It's recommended for everyone 6 months and older, and it lowers the chance of getting very sick even if you do get the flu.

• Get a flu vaccine every year, ideally by the end of October
• Stay away from people who are sick, and stay home when you're sick
• Cover coughs and sneezes with a tissue, then throw it away
• Wash your hands often with soap and water, or use hand sanitizer
• Avoid touching your eyes, nose, and mouth
• Bring in fresh air or gather outdoors when you can

Which doctor treats this

• Start with your primary care provider (family doctor or internist).

Back to school, work, or sports

• Stay home until you've had no fever for 24 hours without fever medicine and you're feeling better.
• For the next 5 days, wash hands often and wear a mask around others.

Children, pregnancy, and older adults

• Babies and children: Call right away for any fever in a baby under 12 weeks. Children under 5 are more likely to get very sick, so call early. Never give aspirin to a child or teen. Flu medicine is safe for children, and oseltamivir can be given to babies older than 2 weeks.
• Pregnancy: The flu can be more serious during pregnancy and for 2 weeks after giving birth. Call your healthcare professional at the first sign of the flu. The flu vaccine is recommended during pregnancy and also protects the baby after birth.
• Older adults: Adults 65 and older are at the highest risk of serious problems. Call early if you get sick, and ask about the flu vaccines made for older adults.

Pregnancy and breastfeeding

• If you're pregnant or planning to be, tell your prenatal provider about this condition.
• Some infections can pass to the baby during pregnancy or birth. Tell your provider if you've been exposed.
• Don't start or stop any medicine on your own. Some are safe in pregnancy and some need to be changed.
• Ask before taking any pain reliever. The FDA advises avoiding ibuprofen and naproxen after 20 weeks unless your doctor says to.
• Breastfeeding: Most medicines are fine, but ask. The NIH LactMed database lists what's known about each one.

Outlook

Most people recover in a few days to under 2 weeks. A cough and tiredness can last longer. Some people, especially those at higher risk, get serious problems like pneumonia. Getting care early and starting flu medicine soon helps lower that risk.

Myths and facts

Getting ready for your visit

If you need to see a healthcare professional, a little preparation helps. Many offices can see you by video, which keeps you from spreading the flu.

What to bring

• When your symptoms started, and your highest temperature
• All medicines you take, including over-the-counter medicines, vitamins, and supplements
• Any long-term conditions, and whether you're pregnant
• Whether you got a flu vaccine this season

Questions to ask

• Should I take a flu medicine?
• Do I need a test for the flu or COVID-19?
• Should the people I live with get flu medicine to prevent it?
• When is it safe to go back to work or school?

Research studies

Research studies test new ways to find and treat health problems. Some are looking for volunteers. Talk with your doctor before joining one.

Search ClinicalTrials.gov for studies on Influenza (flu)