Since 1945, the three strains of influenza viruses considered the strongest have been the ingredients of that year's flu vaccine. Recommended for seniors, children, caregivers and the chronically ill, the shots (and in 2003, the nasal spray) have become the primary defense against the Type A and B flu viruses, which are the eighth leading cause of death in the U.S. annually. The second line of defense is to wash your hands. Viruses are spread through sneezes and coughs that spread droplets on all surfaces within three feet. Depending on the strain and the surface, flu viruses can survive outside a host from a few seconds to more than two weeks.

Viral Survival

Mayo Clinic internist James M. Steckelberg, M.D, says the time flu viruses can survive outside a host depends on the strain and the surface. They can survive from seconds up to 48 hours and generally live longer on hard surfaces (doorknobs, keyboards, cell phones, toothbrushes) than porous ones like fabric or paper. University of Michigan epidemiologist Allison Aiello says viruses live on skin for up to five minutes.

The UK National Health Service says flu viruses can live on a hard surface for up to 24 hours and a soft surface for around 20 minutes. In 2008, Yves Thomas and colleagues at the University Hospital of Geneva found flu viruses thrive in wet environments. Viruses applied to Swiss franc notes survived up to 72 hours, but mixed with human mucus, one Type A strain remained active for 17 days.

Virus life cycle

Viruses are tiny capsules that contain genetic material. To reproduce, they invade cells in your body, taking over the machinery that makes cells work and eventually destroying the host cells. They cause diseases from AIDS to the common cold and are unaffected by anitbiotics.

The Mayo Clinic advises that if you have swine flu or seasonal flu, stay home from work or school and avoid public gatherings until your fever is gone for 24 hours. This should happen within three to five days, unless your infection is unusually severe.

Prevention

The Mayo Clinic says viruses live everywhere--in the air, on food, on plants and animals, in the soil, in water and just about every other surface, including your own body. Most germs won't harm you; your body's immune system protects you against infectious agents. Influenza viruses are highly infectious because they change (mutate) constantly to get past your immune system's defenses. That is why the flu vaccine changes every year.

Besides vaccinations, prevention means avoiding infected persons, wearing masks and handwashing. Masks work in two ways. They must be reasonably tight fitting to filter some of the air you breathe. They also protect your nose and mouth if rubbed with hands that have touched the virus. Cleaning surfaces like doorknobs, desktops and phones frequently will also prevent infection.

Effective Hand Washing

According to the Centers for Disease Control, hand hygiene is the most important tool for preventing infection. Hands should be washed with soap and water frequently to kill the flu virus. Apply soap to hands moistened with warm water. Spread soap to all surfaces and scrub for 15 to 20 seconds. Rinse thoroughly and then dry with a clean paper towel or air dryer (use the paper towel to turn off the taps and on the doorknob).

To protect yourself from flu viruses, do this before preparing or eating food, after coughing or sneezing, after changing a diaper, blowing your nose or using the toilet. If soap and water aren't available, use alcohol-based hand-sanitizing gels.

Transmission

Flu season looms every year from October to May. Five to 20 percent of the U.S. population gets the flu, about 36,000 people (mostly over 65) die and 148,000 are hospitalized. When a flu victim coughs or sneezes into their hand, mucus droplets with the virus within them are transferred to everything that person touches. If you touch these surfaces and touch your face, the virus can enter your system and you can become infected.

Flu develops between two and five days after infection. People are most contagious after developing the symptoms and should stay home and restrict their contact with people. They can continue to shed the virus for up to five days until their symptoms are gone.

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