Influenza

What Happens

Influenza (flu) usually comes on suddenly. In many cases you can pinpoint the hour when symptoms started. Symptoms develop 1 to 4 days after you are infected.

• Classic flu involves fever for about 3 days, followed by a gradual decrease in other symptoms. Fever is usually slightly lower on the 2nd and 3rd days. It may last up to 8 days.

• Respiratory symptoms (cough, runny nose, sore throat) become more noticeable as fever and other symptoms decrease. They usually last 3 to 4 days after the fever goes down. A dry, hacking cough may linger for up to 10 days after other symptoms are gone.

• Complete recovery may take 1 to 2 weeks or longer. Fatigue and weakness can last for several weeks.

• Complications of influenza may develop in anyone, but they are much more likely in older adults and people who have other health problems, especially heart and lung diseases.

Cause

The influenza virus causes the classic flu. Health professionals classify the virus as influenza type A and type B, each of which includes several subtypes or strains. These strains are different from the original virus but retain some of its characteristics.

Type A is usually responsible for the annual outbreaks that typically occur in the late fall and early winter.

The influenza virus changes often, so having flu caused by one strain does not give you full immunity to other strains.

• Widespread outbreaks of the flu usually follow significant changes (called antigenic shifts) in the virus. These epidemics occur about every 10 years. People who get the flu tend to become much sicker when a shift in the flu virus occurs.

• Minor changes in the virus (called antigenic drifts) occur nearly every year.

The virus is spread from person to person through:

• Small droplets that form when a person sneezes or coughs.

• Contact with objects such as handkerchiefs that have been in contact with fluids from an infected person's nose or throat.

• Direct contact, such as shaking hands.

Prevention

You can help prevent influenza by getting immunized with an influenza vaccine each year, ideally in October or November. The inactivated influenza vaccine, commonly known as the "flu shot," is given by injection. This form of the vaccine effectively prevents most cases of the flu, although success rates vary according to age, health status, and how closely the virus strains contained in the vaccine match those that are circulating through the population.

Even if a flu shot does not prevent the flu, the vaccine can reduce the severity of flu symptoms and decrease the risk of complications. Studies have found that the flu shot results in fewer days missed from work and fewer visits to a doctor for respiratory infections, and it reduces the number of people who develop complications from the flu, such as pneumonia. 1 

Other ways to reduce your risk of getting the flu or developing complications

Increase your chance of staying healthy by:

• Washing your hands often, especially during winter months when the flu is most common.

• Keeping your hands away from your nose, eyes, and mouth. Viruses are most likely to enter your body through these areas.

• Eating a healthy and balanced diet.

• Getting regular exercise.

• Not smoking. Smoking irritates the lining of your nose, sinuses, and lungs, which may make you susceptible to complications of the flu.

What won't prevent the flu or shorten its duration

You cannot prevent the flu or make yourself better faster by taking:

• Antibiotics. Taking antibiotics will not treat viral infections such as the flu or prevent complications. If a bacterial infection such as an ear or sinus infection develops after the flu, antibiotics may be helpful.

• Large doses of vitamins and minerals such as vitamin C or zinc or herbal remedies such as Echinacea. They will not prevent or treat the flu.