Me again..... here's some info on the Influenza virus.:
Influenza ('flu)
Influenza is a virus which causes a severe form of respiratory tract infection with generalised bodily symptoms. It spreads around the world in epidemics and is responsible for much ill health as well as many deaths.
Symptoms
If you start to develop cold symptoms but starting more rapidly and rather more violently, with higher fever and severe aches and pains, often in the back and muscles, then you may well be developing influenza. This may be associated with severe headache, cough, and, as a result of the fever, intermittent sweating and shivering. Sometimes there is a gastrointestinal element, with vomiting and/or diarrhoea.
Many people think they have had "flu" when all that they have suffered is a bad cold. When you have influenza you will know the difference. Most people will find it impossible to leave their bed and feel terrible.
The worst symptoms usually last for three to five days, and then should begin to improve. It is common to need two to three weeks off work as there is considerable debility left after the feverish illness is over. Do not be surprised to be quite depressed, this is a natural after-effect of the condition.
Influenza makes everyone feel terrible, but most people recover. It does however have a small, but significant mortality, especially in the very young, the very old, and those with poor immunity.