Good gracious MikeL2, you could have succumbed to that flu virus and no-one would have known for days!

I remember in I think the late seventies getting 'Russian flu'. I lived alone then, and found myself lying on the kitchen floor in the middle of the night, hallucinating that flying creatures were zooming overhead. I was so hot I was lying in a lake of perspiration, with all my cats sitting round me peering at me with interest. I crawled on my stomach to the landline and managed to ring a neighbour, who got a doctor. It lasted a few days, then I felt very weak afterwards. But since then, I don't get either colds or flu, so my immune system must be quite strong.

Iains, you always come up with the most interesting scientific links!
I gather from this one that contact with the 1918 flu virus in early life either reinforced immunity, or (which is most unfortunate) made the person even more vulnerable and brought about their death.
Viruses are weird things. As I understand it, they use our actual DNA to replicate. I wonder if they will finally do away with humans on Earth?