As I understand it the cold is generally bad for viruses and bacteria. It certainly isn’t optimal for reproduction. I know being cold can impact you immune system a bit and people tend to crowd inside when it is cold outside meaning they can spread more easily person to person. Are there other reasons colds seem spread more in the winter than summer?
In: Biology
Cold viruses (typically rhinoviruses) are not seasonal and are actually *less* common during winter months than other times of the year. This is because they’re actually displaced by influenza viruses which are seasonal. Flu viruses are less stable and subject to more environmental considerations for transmission, and overall transmission is greater during these periods due to human behavior, temperature, and humidity.
From what I understand, the primary factor in the spread of the flu is human behavioural changes according to the seasons. For example, in the fall, kids and teens go back to school, spread the germs, then take the germs back to their families, leading to a boom. Same thing happens around the holidays. Conversely, in the summer, people vacation more, and are not forced into huge gatherings where germs can spread rapidly.
The school cycle is doubly important as it is often children who do not practice proper handwashing, coughing, or other sanitary techniques. At least compared to adults who are usually a little more aware of it. Other factors like slightly lower body temperature are practically insignifigant compared to human behaviour.
Partially, it’s, as you identified, that we crowd together more in winter. It’s also thought that colder air has less water-carrying capacity, so the drier air allows airborne diseases (especially flu) to flourish.
Read more: https://www.bbc.com/future/article/20151016-the-real-reason-germs-spread-in-the-winter
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