Influenza, commonly known as "the flu," is a highly contagious viral infection of the respiratory tract. Although the flu affects both sexes and all age groups, kids tend to get it more often than adults. The illness even has its own season — from November to April, with most cases occurring between late December and early March.

Signs and Symptoms

The flu is often confused with the common cold, but flu symptoms tend to develop quickly (usually 1 to 4 days after a person is exposed to the flu virus) and are usually more severe than the typical sneezing and stuffiness of a cold.

Symptoms of the flu may include:

• fever
• chills
• headache
• muscle aches
• dizziness
• loss of appetite
• tiredness
• cough
• sore throat
• runny nose
• nausea or vomiting
• weakness
• ear infection
• diarrhea

Infants with the flu may simply seem sick all of a sudden or "just don't look right." The flu that people get is not the same strain of virus as the avian flu.

Duration

After 5 days, fever and other symptoms have usually disappeared, but a cough and weakness may continue. All symptoms are usually gone within a week or two. However, it's important to treat the flu seriously because it can lead to pneumonia and other life-threatening complications, particularly in infants, senior citizens, and people with long-term health problems.

Contagiousness

Spread by virus-infected droplets that are coughed or sneezed into the air, the flu is contagious. People infected with the flu are contagious from a day before they feel sick until their symptoms have resolved (usually about 1 week for adults, but up to 2 weeks for kids).

The flu usually occurs in small outbreaks, but epidemics tend to occur every few years. Epidemics (when the illness spreads rapidly and affects many people in an area at the same time) peak within 2 or 3 weeks after the first cases occur and then begin to decrease.

About the Flu Vaccine

The flu vaccine usually is offered between September and mid-November, although it may be given at other times of the year. It reduces the average person's chances of catching the flu by up to 80% during flu season. Because the vaccine prevents infection with only a few of the viruses that can cause flu-like symptoms, it isn't a guarantee against getting sick. But even if someone who's gotten the shot gets the flu, symptoms usually will be fewer and milder.

Given as one injection in the upper arm, the vaccine contains killed flu viruses that will not cause the flu, but will prepare the body to fight off infection by the live flu virus. Getting a shot of the killed virus means a person is protected against that particular type of live flu virus if he or she comes into contact with it.

People who got the vaccine last year aren't protected from getting the flu this year because the protection wears off and flu viruses constantly change. That's why the vaccine is updated each year to include the most current strains of the virus.

Kids under 9 who get a flu shot for the first time will receive two separate shots a month apart. It can take up to 1 or 2 weeks after the shot for the body to build up protection to the flu.

Getting the shot before the flu season is in full force gives the body a chance to build up immunity to, or protection from, the virus. Although you can get a flu shot well into flu season, it's best to try to get it earlier rather than later. However, even as late as January there are still 2 or 3 months left in the flu season, so it's still a good idea to get protection.

Who Is Considered High Risk?

In times when the vaccine is in short supply, certain people need it more than others. The Centers for Disease Control and Prevention (CDC) often will recommend that certain high-risk groups be given priority when flu shot supplies are limited. The CDC does not anticipate a shortage this year, but it's difficult to predict how many doses will be used. Call your doctor or local public health department about vaccine availability in your area.

The American Academy of Family Physicians (AAFP), the American Academy of Pediatrics (AAP), and the CDC currently recommend that these high-risk groups be given the flu shot:

• kids 6–59 months old
• anyone 50 years and older
• women who will be pregnant during the flu season
• anyone who lives or works with infants under 6 months old
• residents of long-term care facilities, such as nursing homes
• any adult or child with chronic medical conditions, such as asthma
• health-care personnel who have direct contact with patients
• kids ages 6 months to 18 years on long-term aspirin therapy
• out-of-home caregivers and household contacts of anyone in any of the high-risk groups
  

People who should not get the flu shot include:

• infants under 6 months old
• anyone who's severely allergic to eggs and egg products (ingredients for flu shots are grown inside eggs, so tell your doctor if your child is allergic to eggs or egg products before he or she gets a flu shot)
• anyone who's ever had a severe reaction to a flu vaccination
• anyone with Guillain-Barré syndrome (GBS), a rare condition that affects the immune system and nerves
• anyone with a fever
  

A non-shot option, the nasal mist vaccine, came on the market in 2003 and is now approved for use in 5- to 49-year-olds. But it isn't for everyone and can't be used on high-risk kids and adults. Check with your doctor to see if your child can — or should — get this type of flu vaccine.

Preventing the Flu From Spreading

There's no guaranteed way — including the vaccine — to prevent anyone from getting the flu. Avoiding large crowds can help, but it's often impossible to keep kids cooped up.

Here are some practical ways to help prevent the spread of the flu:

• Wash your hands thoroughly and frequently.
• Never pick up used tissues.
• Never share cups and eating utensils until you're better.
• Stay home from work or school when you're sick with the flu.
• Cover your mouth and nose with a tissue when you cough or sneeze.

Treatment

Cases of the flu rarely require specific medical treatment. But some kids with chronic medical conditions may become sicker with the flu and need to be hospitalized, and flu in a newborn can be dangerous. For a severely ill child or one with other special circumstances, a doctor may prescribe an antiviral medicine that can ease flu symptoms, but only if it's given within 48 hours of the onset of the flu.

These at-home tips can help most otherwise healthy kids cope with the flu. Have them:

• drink lots of fluids to prevent dehydration
• get plenty of sleep and take it easy
• take acetaminophen or ibuprofen to relieve fever and aches (but do not give aspirin unless your doctor instructs you to do so)
• wear layers, since the flu often makes them cold one minute and hot the next (wearing layers — like a T-shirt, sweatshirt, and robe — makes it easy to add or subtract clothes as needed)

When to Call the Doctor

Call the doctor if your child:

• has flu symptoms or the symptoms get worse 
• has a high temperature for more than a few days
• seems to get better, but then feels worse than before

For the most part, though, the flu is usually gone in a week or two with a little rest and tender loving care.

Reviewed by: Larissa Hirsch, MD
Date reviewed: October 2006
Originally reviewed by: Barbara P. Homeier, MD