Immunity is not seasonal

We might pay more attention to the health of our immune systems in winter when colds and flu are all around us. But the truth is, our immune systems have to work hard all through the year, whether it’s to protect us from a flu virus or from other infections that could happen any time. ^7a

Colds and flu are both caused by viral infections of the upper respiratory tract and are probably the most frequent infections we experience through our lifetimes. One reason for this is that there are around 160 different ‘serotypes’ of the rhinovirus family which commonly cause colds. This makes it possible for us to have several colds one after another. Viral DNA changes frequently which makes the job of our immune system quite difficult and also explains why we tend to get many throughout our lives. Children could have 3-8 viral respiratory illnesses a year, and adults 2-4 colds annually. ^{8a, 9a}