Why do people get more colds and flu in winter?

During winter we often stay indoors in poorly ventilated areas and this aids airborne transmission of the virus. | Photo credit: Usman Yusuf

It is believed that the biggest reason for the huge increase in cold cases is the students returning to schools and colleges.

Q: Why do people get more colds and flu in winter? Do viruses spread more easily in moist air, do people’s immunity decrease due to the cold and lack of sunlight, or do viruses simply take advantage of the fact that we spend more time indoors?

Answer: There is no one reason why we get colds and flu in winter. Rhinovirus, which is responsible for up to 40% of colds, thrives better at a temperature of 32°C than the normal body temperature of 37°C. However, 32°C is the normal temperature of the nasal lining, which is good news for the virus.

During winter we are often indoors in poorly ventilated areas and this helps in airborne transmission of the virus. Similarly, ultraviolet rays will kill the virus and this could be another factor as there is obviously very little sunlight in winter.

However, it is thought that the biggest cause of the huge increase in cases at the start of autumn and in the winter just after Christmas is due to schoolchildren and students returning to schools and colleges.

Children and teens are more susceptible to infections because as they grow older, their immune systems learn to fight more infections, and they are exposed to the 200 or more viruses responsible for the common cold.

Nurseries, schools and colleges in densely populated areas are ideal breeding grounds for the virus, which spreads through the community aided by the cool damp weather.