I have a theory that we are exposed to viruses and pathogens all the time, some more contagious than others, and if we have a healthy immune system, they do us no harm. If our immune system is weak, due to lack of nutrition, lack of exercise, lack of sunlight or emotional problems (such as holding on to anger or grief), we are then unable to fight off the pathogen, and we get sick.

I think that's why so many people died from Spanish Flu 100 years ago. In the UK, there were so many undernourished people at that time, it was difficult to find healthy men to fight in the First World War. On top of that, people were being wounded in war, suffering post-traumatic stress and losing friends and relatives on the battlefield. People's immune systems must have been shot to bits.

Keeping people indoors with the mainstream media feeding them a constant stream of fearmongering sensationalism is the worst way to beat any disease.

Also I do think that pollution makes it worse and could be responsible for many of the really serious cases.