The reasons behind the seasonal pattern are unclear, but may be due to:
* prolonged periods spent indoors and in close contact with others during periods of wet and/or cold weather
* increased viability of the influenza virus (A and B) on exposed surfaces (doorknobs, countertops, etc.) in low humidity and low temperature conditions
* cold temperatures lead to drier air, which may dehydrate mucus, preventing the body from effectively expelling virus particles
* effect of vitamin D levels on immunity to the virus [2]; vitamin D levels fall when people stay out of the sun.
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http://www.influenzaworld.com/portal/eipf/pb/t/iwhcp/types_of_influenza
The reasons behind the seasonal pattern are unclear, but may be due to:
* prolonged periods spent indoors and in close contact with others during periods of wet and/or cold weather
* increased viability of the influenza virus (A and B) on exposed surfaces (doorknobs, countertops, etc.) in low humidity and low temperature conditions
* cold temperatures lead to drier air, which may dehydrate mucus, preventing the body from effectively expelling virus particles
* effect of vitamin D levels on immunity to the virus [2]; vitamin D levels fall when people stay out of the sun.