Part of the show Was Swine 'Flu Man-Made?
Why is flu more prevalent in winter?
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 doesnít mean it goes away completely in summer but it does come much more commonly in winter.
We think thatís 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, itís 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 thatís 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.
There are a number of factors.
I think its because most people's immune system to prone to various pathogens. In the winter, people tend to gain more pounds and eat heavier. Unlike in the summer, people are more active and eat less. Also, the cold weather does have an effect on viral infections as well, where it is easily spread Jonathan Madriaga, Wed, 25th Nov 2009
Lower humidity in winter means drier membranes in the nasal passages and throat. In the former at least, this commonly causes cracking and bleeding (more bloody discharge in winter for sure), which would seem to afford easier direct entry points into the blood stream for virii. And simply drier membranes means smaller positive flow (outward) of protective mucus current, and this could give passage for virii to diffuse inward.
Absolutely its the falling levels of vitamin D3 that makes people so susceptible to flu and colds in the winter.
I do not get the flu nor head colds and I keep windows open year round, spend little time in unventilated places even in winter, and do not go where people gather simply because I dislike most people. It makes sense except that if this were absolutely true the flu would still happen in summer sometimes. I never hear of a single case in summer, it must still happen though? I hate it on buses and trains when others want windows closed and complain its cold. Who cares? We need air circulation! No wonder these idiots are always ill. I could care less abt keeping heat in, I want germs out! Another thing, overweight people do not have lowered immune systems, in general. I totally disagree with other poster here. Immunity is regulated by unrelated things, so that is not why in winter people get ill, because they eat more, that is silly. Kayfabe, Sun, 25th Sep 2016