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. Because 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 five and adults older than 65. The risk for the flu also increases if you have a weak immune system or if you have a chronic illness, such as:

  • heart disease
  • kidney disease
  • diabetes, type 1 and type 2

In the beginning, the flu can mimic a common cold. Early symptoms may include a sore throat, sneezing, or a runny nose. Symptoms often worsen as the virus progresses:

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

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

However, you can ask your doctor about antiviral drugs. Taken within the first 48 hours of symptoms, antivirals can reduce the length and severity of the flu.

Complications 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. This is why it can spread quickly in households, schools, offices, and among groups of friends.

According to the U.S. Centers for Disease Control and Prevention (CDC), it’s possible to infect 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 pass the virus to someone before you realize that you’re sick.

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

You can also get 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 sick people.

There are three different types of flu viruses: type A, type B, and type C. Type A flu can infect animals and humans. This virus constantly evolves and can cause annual flu epidemics.

Type B flu can also cause seasonal outbreaks during the winter months, but this type is typically less severe than type A and causes milder symptoms. Occasionally, type B can cause severe complications. Whereas type A flu is caused by different strains, type B flu is caused by one strain of the flu.

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

Because of the risk of complications, it's important to protect yourself and your family from the virus. Since the flu virus can spread 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’s sick with 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. The vaccine protects against common strains of the flu virus. Although the vaccine isn’t 100 percent effective, it can reduce the risk of flu by 50 percent to 60 percent, says the CDC.

The flu vaccine is administered by injection in the arm. The CDC no longer recommends nasal spray flu vaccinations.

The flu virus changes from year to year. Vaccines provide protection against the most common strains of the flu for each particular year. The flu vaccine works because it stimulates 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 an injection of the flu vaccine, your body begins production of 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. Understand, 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.
  • Let your doctor know 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 office and home