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The Flu (Influenza)

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What Is the Flu?

The flu is an infection of the respiratory tract (nose, throat, and lungs). It's caused by a virus that spreads easily from person to person. Flu viruses usually cause the most illness during the colder months of the year. In the United States, flu season is from October to May.

What Are the Signs & Symptoms of the Flu?

When people have the flu, they usually feel worse than they do with a cold. Most people start to feel sick about 2 days after they come in contact with the flu virus. They might have:

Babies with the flu also may suddenly seem fussy or just "not look right."

What Causes the Flu?

The flu gets its name from the virus that causes it — the influenza virus. It spreads when people cough or sneeze out droplets that are infected with the virus and other people breathe them in. The droplets also can land on things like doorknobs or shopping carts, infecting people who touch them.

Is the Flu Contagious?

The flu is very contagious. People can spread it from a day before they feel sick until their symptoms are gone. This is about 1 week for adults, but it can be longer for young kids.

The flu usually happens in annual epidemics. An epidemic is when an illness spreads quickly and infects lots of people in an area at the same time. Some years the epidemic is more severe and widespread than others. An epidemic that spreads worldwide is called a pandemic. This is far less common. There were three influenza pandemics in the 20th century, and one so far in the 21st century, in 2009 with influenza A (H1N1).

How Is the Flu Diagnosed?

Often, how a child looks is enough for health care providers to diagnose the flu. Kids who have it usually look ill and miserable.

Other infections can cause symptoms similar to the flu. So if health care providers need to be sure that someone has influenza, they might do a test. They'll take a sample of mucus by wiping a long cotton swab inside the nose or throat. Results might be ready quickly, or can take longer if the test is sent to a lab.

How Is the Flu Treated?

Most kids with flu get better at home. Make sure your child:

  • drinks lots of liquids to prevent dehydration
  • gets plenty of sleep and takes it easy
  • takes acetaminophen or ibuprofen to relieve fever and aches. Don't give kids or teens aspirin because of its link to Reye syndrome.
  • wears layers that are easy to remove. Kids might feel cold one minute and hot the next.

Children with the flu should stay home from school and childcare until they feel better. They should go back only when they haven't had a fever for at least 24 hours without using a fever-reducing medicine. Some kids need to stay home longer. Ask the doctor what's best for your child.

Doctors may prescribe antiviral medicine for a very ill child or kids are at risk for more serious symptoms. The medicine can shorten the flu by 1–2 days. It works best if children start taking it within 48 hours of the start of the flu. If a doctor prescribes antiviral medicine for your child, ask about any possible side effects. Doctors won't prescribe antibiotics for the flu. Antibiotics work only against bacteria, not viruses.

What Problems Can Happen?

Some people are more likely to have problems when they get the flu, including:

  • kids up to age 5, especially babies
  • people with a weak immune system from medicines (such as chemotherapy or long-term steroid use) or illnesses or illnesses (like HIV infection or cancer)
  • people with chronic (long-term) medical conditions, such as asthma or diabetes
  • kids or teens who take aspirin regularly
  • people who are very obese
  • women who are pregnant, trying to get pregnant, just had a baby, or are breastfeeding
  • people who live in long-term care facilities, such as nursing homes
  • people 65 years and older

If they get the flu, their illness can be more serious. They can develop pneumonia or get even sicker from other kinds of infections (like bacterial infections). If this happens, many will need medical care in the hospital. So it's important for them not to be near anyone who has the flu or flu-like symptoms.

People who have flu symptoms should keep their distance from anyone who might get very sick if they catch the flu.

How Long Does the Flu Last?

Fever and other flu symptoms often go away after a week or so, but some people may still have a cough or feel weak for longer than that.

Can the Flu Be Prevented?

There's no guaranteed way to avoid the flu. But getting the flu vaccine every year can help. Everyone 6 months of age and older should get it each year.

It's best to get the flu vaccine before the end of October, as flu season starts. But even if you don't, you can get vaccinated later while the flu is still going around. Many health care providers give flu vaccines through May if the flu virus is still circulating.

If your child is sick, has a fever, or is wheezing, talk to your doctor to see if you need to reschedule the flu vaccine.

As with many germs, washing hands well and often, wearing a mask, and avoiding contact with sick people can help protect someone from getting sick.

What Else Can Help?

If someone in the family has the flu, they can help prevent spreading it by:

  • Never sharing cups and eating utensils.
  • Staying home from work or school until they're better.
  • Covering their mouth and nose with a tissue when they cough or sneeze, then putting it in the trash.
  • Coughing or sneezing into their upper arm, not their hands, if a tissue isn't handy.
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Date reviewed: November 2022