Outbreaks of influenza typically occur in the winter, when the environment features colder air with a low water content, or low humidity. In fact, air in the winter can have as much as four times less moisture than air in the summer. And the flu likes dry air.

This could be another explanation of the seasonal nature of flu. In this case, researchers are talking about absolute humidity, not relative humidity, the more common reading. Relative humidity is a ratio not an absolute amount. Absolute humidity, on the other hand, is the actual amount of water in a volume of air. And it is the amount of water that concerns the virus. It seems that the water in the air affects the virus itself, although the exact mechanism is not clearly understood.

What is clear is the discovery that when the absolute humidity is low, that is to say the air is dryer; the survival rate of the virus is greater. Longer survival equals more transmission, meaning higher infection rates.

Once the numbers were analyzed, it was seen that more flu cases were discovered when it was both colder and drier. In temperate regions of North America and Europe, absolute humidity has a powerful cycle that is seasonal. These changes, which dramatically lessen in the wintertime, parallel an increase in the rates of transmission of the virus as well as the rate of survival of that same influenza virus.

By using absolute humidity in this way, an additional factor in the spread of influenza and the endurance of the virus can be an added to the creation of models of infection, or models for the prediction of viral spread. Doctors Shaman and Kohn, authors of a study published in the Proceeds of the National Academy of Science on March 3, 2009, were quick to point out that this is a preliminary study and further exploration of this phenomenon is needed, especially in the areas of epidemiology, modeling and lab work into the actual structure of the virus.

Still, this remains an important potential insight into the way the flu virus is spread, and consequently how to keep the flu virus from spreading. Until all mechanisms of flu infection are better understood, the flu vaccine remains the best protection against becoming infected.

With the memory of last years absences and doctor's visits because of the flu fresh in your mind, you are determined to take extra precautions this year. You are ready to line up for this year's flu shot as soon as you can. But wait—wasn't there some concern over preservatives in flu shots? Well, there is good news on this front. Preservative-free flu shots are available for you and your loved ones.

These new type of flu shots have already been approved by the FDA and are on the market. The preservative Thimerosal has been removed from many vaccines already, and a public push by several activist groups is forcing vaccine manufacturers to remove this mercury based additive from all new vaccine formulations.

Flu vaccines were among the last to have this preservative removed but, thimerosal free flu vaccines are out there. Be warned, however, you may have to do a bit of searching to find them. Be sure to call the physician's office before you go in for the shot, See if they even offer this option. If they don't, ask them to order the vaccine for you. And remember; do not be afraid to take your business elsewhere. More and more preservative free vaccines are being manufactured every day, but they won't reach the public until physicians begin ordering them. Use your purchasing power to make your physician responsive to your needs.

Aventis-Pasteur has a preservative-free vaccine approved for pediatric use. For older children and adults, there are two options: a single dose flu injection by Chiron, or the vaccine Flumist which you can request by name. Flumist is a nasal spray vaccine manufactured as a cooperative venture by Wyeth Pharmaceuticals and Medimmune. Among those using Flumist, there have been some reports of respiratory symptoms in patients with have pre-existing breathing problems.

The link between thimerosal and the drastic consequences that have brough this issue to the fore are still developing. But this is an important enough issue that there is reason to take advantage of an opportunity to be that much safer in your choices about your health.

According to the results of a new study that was just made available online by the Journal of the American Medical Association (JAMA), people who plan to take Tamiflu to prevent catching the flu, or to limit symptoms and the duration of the illness if they have already become infected with the flu, should probably make other plans. According to the results of this study, there are now flu strains resistant to Tamiflu.

The strain of flu that is circulating in the U.S. that is showing resistance to Tamiflu is the H1N1 strain. According to the Atlanta-based U.S. Centers for Disease Control and Prevention (CDC), this is the most common type of flu this year.

Last year, Tamiflu resistance was found in only 12 percent of the strains circulating. This year, 98.5% of H1N1 flu strains are resistant to Tamiflu. Terence Hurley, a spokesman for Roche who manufacturers Tamiflu, emailed a statement which emphasized the fact that flu viruses constantly mutate while the types of strains circulating among the population change as well.

According to the CDC's Alicia Fry, head researcher for the above-referenced study, the use of Tamiflu itself has not led to the development of these resistant strains. The Tamiflu resistance researchers discovered is not the same as bacterial resistance to antibiotics which develops through misuse or overuse. The ability of flu viruses to mutate is why a new vaccine must be developed each year.

According to the World Health Organization, between 5 and 15 percent of the world's population comes down with the flu each year. Between 250,000 and 500,000 people die from the flu each year. According to Fry, “The vaccine is still the best form of prevention. We also know that these strains [resistant to Tamiflu] are susceptible to other antiviral drugs.”

The strains resistant to Tamiflu do not show any resistance to Relenza (made by GlaxoSmithKline). The CDC is recommending that people who are suffering from the flu take Relenza or generic rimantadine along with Tamiflu.

According to the CDC, November through March is prime flu season in the U.S. According to Fry, this year's flu vaccine is a good match to the strains that are circulating. The flu vaccine is developed anew each year to provide protection for the upcoming flu season.

The media attention given to influenza has clothed this disease in the fabric of modernity. But influenza is, in fact, a very old disease that dates back thousands of years and varies in lethality from year to year and outbreak to outbreak.

In ancient Greece, Hippocrates described the symptoms of flu roughly 2400 years ago. For historical events such as these, we primarily have descriptions of symptoms rather than accurate diagnoses or demographic data. This makes it hard to accurately pinpoint ancient flu pandemics. One of the earliest records of an outbreak that can be linked to influenza was in 1580. It began in Russia and ultimately spread to Europe by way of Africa. One of the more virulent strains, this influenza killed 8,000 people in the city of Rome alone. Many villages in Spain were totally decimated.

Pandemics seem to hit about every century. There were periodic outbreaks in the 17th and 18th centuries. The pandemic of 1830 was especially widespread. It was also particularly infectious, and one out of four people exposed, or 25%, contracted the disease after exposure.

But the most infamous of all influenza outbreaks was the pandemic of 1918. Estimates for the number killed in this outbreak were between 20 and 100 million people. The wide range in the estimate is due to the global nature of this outbreak. This outbreak reached far flung Pacific Islands and the Arctic.

Not only did this strain of influenza have an extremely high infection rate—over 50% of people exposed contracted the disease—but the symptoms were especially severe. Hemorrhaging from the mouth, nose and intestines were common, as were hemorrhages under the skin. A majority of deaths were from secondary infections like pneumonia, but the virus killed directly with massive bleeding and swelling.

Another unusual feature was that the highest mortality rate was among young, otherwise healthy, adults. This was linked to a cytokine storm, which is a condition where the normal antibody/cytokine cascade is not stopped by the body’s own processes. It is as if the body over responds to the contagious agent, making so many antibodies that they begin to harm the body. Say this happens in the lungs. The lungs will fill with fluid and suffocate the patient before the virus can kill the patient.

Having established that the 1918 pandemic was bad, just how bad was it? It is estimated that between 2.5% or more of the entire world’s population was killed. To put in another way, in the first 25 years of the AIDS epidemic, 25 million people died. In 1918, over 25 million died in 25 weeks.

In the U.S. there are limited options for people who want a preservative-free flu vaccine. For children between 6 and 23 months, Aventis-Pasteur makes a preservative-free version of this vaccine. For older children and adults, there are two choices: FluMist, a nasal spray vaccine created by a partnership between Wyeth and MedImmune, and a single-dose injection made by Chiron Corp.

The flu vaccines were, generally, the last of the common vaccines to offer versions without added mercury. They are hard to find and have to be specifically requested in most places. Many doctors' offices say that the preservative-free flu shots are more expensive and harder to store. If there is an accessibility issue, it is not due to supply, but rather to a resistance on the medical community to order the preservative-free vaccines.

Although mercury, in the form of thimerosal, has been removed from most vaccines, vaccines may still contain aluminum, formaldehyde, human serum albumin, gelatin, antibiotics and yeast proteins. Some of these compounds are purported to aid the vaccine in establishing an immune response. Others are solely there as preservatives, guarding against contamination of multi-use vials by the administering medical staff.

The whole question comes down to where you fall on the “How dangerous are preservatives anyway?” continuum. The FDA has walked and is walking a fine like between the pro-vaccine side and the anti-vaccine side. While it supports the sale and manufacture of preservative-free vaccines, it says there is no proven link between preservatives in vaccines and side-effects or sequelae in patients that some claims are a consequence of the vaccines or their components.

There is a gray area in the question of how dangerous these preservatives are. No direct link has yet to be established. The question is do you, as a medical consumer, want to support the medical establishment and take the risk that the nay sayers are wrong? Or do you want to seek out preservative-free flu vaccines and force local doctors to address your concerns?