Colds or what the world needs now is Vicks VapoRub

Here's something that never occurred to me before we moved countries. People always say the common cold has over 110 variants, and that over time you are exposed to and contract them one by one. Each time you come through a cold you gain a certain amount of immunity to that strain so gradually your cold-catching frequency should diminish.

However, while there may be 110 different strains of the cold virus, they are not likely to all be equally prevalent throughout the world at the same time. It stands to reason that some strains are better represented in a given area than others. I imagine that several strains becomes common in a certain area at one time then gradually die out in that area to be replaced by a different group.

Hypothetically speaking, there may be 20 variants of the common cold that are working their way through the UK population right now. Gradually the people will build up resistance to them and stop becoming ill. However, at the same time there are 20 other variants infecting Americans and making them ill. Because I've moved countries, I am now exposed to a whole host of new colds.

Which explains why I and my whole family have been sick ever since we got here.

That's my thesis, can I have a PHD?