Why do people get more colds and flu in the winter? Because it’s colder, windows tend to be kept shut, reducing ventilation and allowing higher viral loads to be present. Reduced levels of ultraviolet light, owing to shorter days and increased cloud cover, reduces viral attrition as well as vitamin D synthesis. Many viruses are vulnerable to the drying effects of sunlight, as well as the radiation.
Sunlight promotes vitamin D production and many countries, the UK included, promote supplementation during winter months. Levels of humidity are also thought to be a component of spread, and this can be affected by the number of people in a room and their proximity. Hand washing, the use of alcohol gels and flushing away you tissues, can reduce cross contamination of hard surfaces, door handles and shared telephones or equipment, like computers.
You might change your habits due to the weather, travelling on public transport, rather than walking to work, eating with others, rather than crossing over to the park and sitting on a bench and so on.
Children are also a good vector for infection, especially when they are younger, as their immune system is still immature and being exposed to new viruses. Winter can lead to children being kept inside, during breaks and they tend to be less concerned with personal hygiene. Then the Apple of your eye comes home and you end up feeling ill over Christmas.
