Hello and Welcome to the SmartMEDinfo Doctor’s Blog with our lead editor, Dr. Moira Dolan, MD!

Here are some little known facts about influenza:

Did you know that there is actually no scientific evidence that influenza is passed from a sick person to a well person. In 2003 researchers made an extensive review of the entire English medical literature and could not find a single study which showed that flu is spread from person to person.

Experiments have shown is that the majority of healthy people experimentally exposed to influenza viruses get no illness or only mild illness. One of the earliest studies that tried to prove that flu is spread by respiratory droplets was done during the great flu outbreak of 1918. Researchers actually took snot from infected people with fevers and injected it into the nostrils of healthy volunteers and could not cause flu illness in any of them.

Studies have shown that over 70% of people who get the flu cannot recall any exposure to a sick person. In families living in the same house as an ill person, anywhere form none to up to a maximum of only 13% of family members will get ill with the flu.

Another thing that has to be explained is why the flu epidemics of the past seemed to “spread” so rapidly in an era before modern fast transportation. We now know that what was probably happening was not “spread”, but simultaneous infection in a particular season, with all countries of a certain latitude and weather pattern being affected at once.

So why do the numbers of people with flu go so high every winter? There must be some “seasonal factor” that dampens immunity. The most obvious change in the winter is that people spend less time outdoors in the sun. Even people with outdoor winter jobs are bundled up and do not get significant sun exposure in the winter.

Sun shining on the skin changes a chemical in the body into active vitamin D. Vitamin D is only found in a very few foods, and most of our D comes from the sun acting on our skin. Vitamin D levels drop dramatically every winter. A recent study reported that over 99% of people who took 2000 IU of vitamin D per day had no seasonal colds or flu.

References

Aloia JF, Li-Ng M: Epidemic influenza and vitamin D. Epidemiol Infect 2007; 135: 1095–1096.

Alford RH, Kasel JA, Gerone PJ, Knight V: Human influenza resulting from aerosol inhalation. Proc Soc Exp Biol Med 1966, 122:800-804.

Beare AS, Craig JW: Virulence for man of a human influenza-A virus antigenically similar to “classical” swine viruses. Lancet 1976, 2:4-5.

Beare AS, Kendal AP, Craig JW: Further studies in man of Hsw1N1 influenza viruses. J Med Virol 1980, 5:33-38.

Brankston G, Gitterman L, Hirji Z, Lemieux C, Gardam M: Transmission of influenza A in human beings. Lancet Infect Dis 2007, 7:257-265.

Bridges CB, Kuehnert MJ, Hall CB: Transmission of Influenza: Implications for Control in Health Care Settings. Clin Infect Dis 2003, 37:1094-1101.

Cannell, John , Michael Zasloff, Cedric F Garlan , Robert Scragg and Edward Giovannucci, On the epidemiology of influenza, Virology Journal 2008, 5:29

Gregg MB: The epidemiology of influenza in humans. Ann N Y Acad Sci 1980, 353:45-53.

Halloran ME, Hayden FG, Yang Y, Longini IM Jr, Monto AS: Antiviral effects on influenza viral transmission and pathogenicity: observations from household-based trials. Am J Epidemiol 2007, 165:212-221.

Jordan EO: Epidemic influenza, a survey Chicago: American Medical Association; 1927.

Thompson WW, Shay DK, Weintraub E, Brammer L, Bridges CB, Cox NJ, Fukuda K: Influenza-associated hospitalizations in the United States. JAMA 2004, 292:1333-1340.