Why is 'flu more prevalent in winter?

13 December 2009

Flu

Flu virus

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Question

Martin asked:

Why is 'flu more prevalent in winter?

Answer

Chris -   Well, we think flu spreads better in winter because of human behaviour because it does this reproducibly in every country in the world and in which it is winter time - it doesn’t mean it goes away completely in summer but it does come much more commonly in winter.

We think that’s because it spreads better in winter because of what humans do.  We go indoors more in winter so there are more people together indoors with the windows closed.  Also, unlike summer time, it’s less light and therefore there's less ultraviolet radiation to dry out the virus and kill it.  So 'flu finds it easier to persist on surfaces spread by coughs and sneezes, and it hangs around for longer.

As a result you have a higher chance of passing it on so that’s what we think goes on.  And then the big determinant, the disproportionate determinant, is the school year.  The long summer school holiday powerfully knocks 'flu on the head because kids stop mixing and spreading the infection amongst themselves.  What normally happens is that they become infected and then go home and give it to their parents and the parents then carry the infection to all of the other parts of the social and age strata, usually through their workplace.

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