How it is spread
The flu virus is spread in the small droplets of saliva coughed or sneezed into the air by an infected person. If you breathe in these droplets, you may become infected.
Flu can also spread if someone with the virus touches common surfaces such as door handles with unwashed hands.

The infectious period
Symptoms develop one to four days (two days on average) after being infected.
People with flu are usually infectious (can spread the virus) a day before symptoms start, and remain infectious for five or six days. Children and people with weaker immune systems (such as cancer patients) may remain infectious for slightly longer.
Try to avoid all unnecessary contact with others during this infectious period.

A video of how flu spreads
This video is quite good, it gives an intro as to how the flu enters your immune system and reproduce itself.

How common is it?
Seasonal flu is a very common illness that occurs every year, usually during the winter months (October to April in the UK).
The number of people who consult their GP with flu-like symptoms varies from year to year, but is usually between 50 and 200 for every 100,000 people. This is in addition to the many people with flu who do not see their GP.

Outlook
Your symptoms will usually peak after two to three days. You should begin to feel much better within five to eight days.
However, elderly people or those with certain medical conditions may develop a complication such as a chest infection. This can lead to serious illness and can be life-threatening.
In the UK, about 600 people a year die from seasonal flu. This rises to around 13,000 during an epidemic.
A seasonal flu vaccine is available free if you are over 65, have a serious medical condition or live in a residential home. For more information see Seasonal flu jab.

A few simple recommendations
1. Get enough sleep: Your immune system functions much better when you get enough sleep. Most people really need about 8 hours per night for optimal health. If you’re body is fatigued, it simply won’t be able to fight off the flu virus (or any other infection) very well.

2. Exercise regularly: Exercise helps keep your immune system strong. In fact, a recent study showed that mice who performed mild exercise as soon as they were exposed to the flu virus had much lower death rates.

3. Avoid sugar: Even small amounts of sugar can significantly impair your immune function, making you more susceptible to a flu infection. A large amount of sugar, such as the amount found in a normal can of soda, hurts your immune function for hours.

4. Drink lots of pure water: Keeping your mucous membranes well-hydrated is a key to helping them fight off viruses. Shoot for about eight 8-ounce glasses per day.

5. Reduce stress: Too much stress has a highly negative impact on your overall health and, over time, it will make you much more susceptible to a flu infection. Studies show that prolonged stress is at least partially responsible for 90% of all illness and disease. Regular exercise and sufficient sleep both help reduce stress levels. Also, meditation is a proven stress-buster that is easy, enjoyable and can be used on a daily basis.

6. Wash your hands often: Also, carry a bottle of alcohol-based hand sanitizer with you and use it frequently, especially after you touch anything that others have touched recently (like doorknobs).

7. Eat immune-boosting foods on a daily basis: A healthy diet, including a few proven immune-boosting foods, is one of the best ways to avoid catching the flu. The best flu-fighting foods are:

Fresh, organically grown fruits and vegetables – Brightly colored fruits and vegetables are packed with healthy phytonutrients that can strengthen your immune system, lowering your susceptibility to the flu virus.
Fresh raw or lightly-cooked garlic – Garlic has strong natural antiviral properties that can help to fight off a flu virus. Also, garlic provides a strong boost to your immune system, especially when eaten on a regular basis.
Green Tea – Like garlic, green tea has shown the ability to both kill viruses and to stimulate the immune system to fight off flu infections, especially when used daily. Try to drink 3-6 cups of strong green tea per day during the flu season.
Cayenne Pepper – Cayenne has a long list of health benefits and is believed to be a mild immune-booster. Also, cayenne contains large amounts of natural vitamin A, considered to be an important “anti-infection” nutrient.

8. Keep your hands away from your face and head: The flu virus enters your body through the eyes, nose, mouth, and possibly even the ears.

9. Get fresh air every day: During the winter the dry heat from indoor heating systems dries out your mucous membranes and makes you more susceptible to viruses. If you can, during the day, crack open a window or two to give your body some relief.

10. Drink little or no alcohol during flu season: Too much alcohol impairs liver and immune function, which leaves you open to all kinds of infections. Heavy drinkers are especially susceptible to flu infections. Also, alcohol dehydrates your body which is always bad during flu season.

11. Don’t smoke and avoid smoke-filled places: First and second-hand smoke significantly impairs your immune system. It also dries out your nasal passages and paralyzes cilia, the small hairs in your nose and lungs that help keep out viruses.

12. Take regular saunas: Many experts believe that taking a sauna several times a week can help to keep you from getting the flu. Many people, especially in Europe, takes saunas just for this reason. The air you breath in a sauna is too hot for cold and flu viruses to survive.

In essence, it’s a substance, usually a protein or carbohydrate, that induces immunity to a disease or infection. You can get immunity to a disease in two different ways.

One is to have the infection and thereafter you have a level of immunity.

The other way is to receive a part of the virus or bacteria that won’t cause an infection, but will allow you to develop antibodies so that when you later get the infection, you will be able to handle it.

The H1N1 flu vaccine falls into the latter category, exposing recipients to a small amount of a purified version of virus, grown in a laboratory, in order to boost the body’s level of resistance to that specific illness.

What is a vaccination and how does it work?
Vaccinations protect you from specific diseases that can make you very sick, disable or even kill you. They boost your body’s own defence system, which is also called the immune system.
Vaccines create immunity that protects you from an infection without causing the suffering of the disease itself.  Sometimes vaccines are called immunizations, needles or shots.

How vaccines work
- Most vaccines contain a little bit of a disease germ that is weak or dead. Vaccines do NOT contain the type of germ that makes you sick. Some vaccines do not contain any germs.
- Having this little bit of the germ inside your body makes your body’s defence system build antibodies to fight off this kind of germ. Antibodies help trap and kill germs that could lead to disease.
- Your body can make antibodies in two ways: by getting the disease or by getting the vaccine. Getting the vaccine is a much safer way to make antibodies without having the suffering of the disease itself and the risk of becoming disabled or even dying.
- Antibodies stay with you for a long time. They remember how to fight off the germ. If the real germ that causes this disease (not the vaccine) enters your body in the future, your defence system knows how to fight it off.
- Often, your defence system will remember how to fight a germ for the rest of your life. Sometimes, your defence system needs a booster shot to remind it how to fight off this germ.
- Sometimes vaccines prevent one disease. Sometimes they are combined to protect you from several diseases with one shot. For example, the MMR vaccine fights Measles, Mumps and Rubella (German measles).

Scientists are looking at new ways to give vaccines, such as by mouth or with nose spray.