Influenza, or the flu, is a viral infection that attacks the lungs, nose, and throat. It’s a contagious respiratory illness with symptoms ranging from mild to severe.

The flu and the common cold have similar symptoms. It can be difficult to distinguish between the two illnesses. In most cases, flu symptoms are more severe and last longer than the common cold.

Anyone can become sick with the flu, but some people have a higher risk for infection. This includes children under the age of 5 and adults ages 65 and older.

The risk of the flu also increases if you have a weakened immune system or if you have a chronic condition, such as:

In the beginning, the flu can mimic a common cold. Early symptoms may include:

  • sore throat
  • sneezing
  • runny nose

Symptoms often worsen as the virus progresses and can include:

  • fever
  • achy muscles
  • body chills
  • sweating
  • headache
  • dry cough
  • nasal congestion
  • fatigue
  • weakness

The flu doesn’t usually require a doctor’s visit. Symptoms often improve with home treatment in about a week. You can relieve symptoms with over-the-counter cold and flu medications. It’s also important to get lots of rest and drink plenty of fluids.

However, some people are more likely to develop complications from the flu. If you or your child is in one of these high-risk groups, seek medical attention as soon as you suspect the flu.

High-risk groups include those who are:

  • under 2 years old
  • 65 years or older
  • pregnant or have recently given birth
  • 18 or younger and taking aspirin or salicylate-containing medications
  • of American Indian or Native Alaskan ancestry
  • have a chronic condition, such as diabetes, asthma, heart disease, HIV
  • living in a nursing home or care facility

Your doctor can prescribe antiviral drugs. Taken within the first 48 hours of symptoms, antivirals can reduce the length and severity of the flu.

Most people recover from the flu without complications. But sometimes, a secondary infection can develop, such as pneumonia, bronchitis, or an ear infection.

If your symptoms go away and then come back a few days later, you may have a secondary infection. See a doctor if you suspect a secondary infection.

If left untreated, pneumonia can be life-threatening.

To protect yourself against the flu, you need to understand how the virus spreads. The flu is highly contagious. It can spread quickly in households, schools, offices, and among groups of friends.

According to the Centers for Disease Control and Prevention (CDC), it’s possible to transmit the flu to someone as early as one day before symptoms begin and up to five to seven days after you become sick.

After coming in contact with the virus, you’ll begin to show symptoms within one to four days. You can even transmit the virus to someone before you realize you’re sick.

The flu is primarily transmitted from person to person. If someone with the flu sneezes, coughs, or talks, droplets from them become airborne. If these droplets come in contact with your nose or mouth, you can become sick too.

You can also contract the flu from handshakes, hugs, and touching surfaces or objects contaminated with the virus. This is why you shouldn’t share utensils or drinking glasses with anyone, especially someone who might be sick.

There are three different types of flu viruses: type A, type B, and type C. Animals and humans can contract type A flu because the flu virus can be transmitted from animals to humans. This virus constantly changes and can cause annual flu epidemics.

Type B flu can also cause seasonal outbreaks during the winter months. However, this type is typically less severe than type A and causes milder symptoms. Occasionally, type B can cause severe complications. Type B can only be transmitted from humans to humans.

Type A flu is caused by different strains. Type B flu is caused by one strain of the flu.

Type C flu only affects humans. It causes mild symptoms and few complications.

It's important to protect yourself and your family from the virus because of the potential for complications.

Since the flu virus can be transmitted from person to person, make sure you wash your hands frequently with soap or use alcohol-based hand sanitizer. Also, avoid touching your nose and mouth with your hands.

The flu virus can live on hard surfaces and objects for two to eight hours. Use disinfectant wipes or spray on commonly touched surfaces in your home or at work to further protect yourself.

If you're caring for someone who has the flu, wear a face mask to protect yourself. You can help stop the spread of the flu by covering your cough and sneezes. It’s best to cough or sneeze into your elbow instead of your hands.

Additionally, consider getting an annual flu vaccination. The vaccine is recommended for everyone over the age of six months. It protects against common strains of the flu virus.

Although the vaccine isn’t 100 percent effective, it can reduce the risk of flu by 40 to 60 percent, according to the CDC.

The flu vaccine is administered by injection in the arm. There’s also a nasal-spray flu vaccine option for non-pregnant individuals between the ages of 2 and 49.

The flu virus changes from year to year. Vaccines provide protection against the most common strains of the flu each year. The flu vaccine works by stimulating the immune system to create antibodies to fight the infection.

To create an effective vaccine, the World Health Organization determines which strains of the flu virus to include in the next year's vaccine. The vaccine contains either an inactive or weakened form of the flu virus.

The virus is mixed with other ingredients, such as preservatives and stabilizers. Once you receive the flu vaccine, your body begins producing antibodies. This helps fight any exposure to the virus.

After getting a flu shot, you may have flu-like symptoms, such as a low-grade fever, a headache, or muscle aches.

However, the flu shot doesn’t cause the flu, and these symptoms typically go away within 24 to 48 hours. The most common complication of the flu vaccine is tenderness at the injection site.

What you can do:

  • Get a flu shot. This will help protect you from life-threatening complications such as pneumonia.
  • It takes two weeks for your body to make flu antibodies after you receive a vaccination. The earlier you get a flu vaccine the better.
  • Tell your doctor if you have a severe allergy to eggs before you get a flu shot. Some forms of the vaccine may contain trace amounts of egg protein.
  • Wash your hands frequently.
  • Cough and sneeze into your elbow.
  • Wipe down frequently touched surfaces in your home and office.