It's a virus' says the doctor. And that's that. You accept the diagnosis, and the inference that there's nothing more to be done, except to wait to get better from it.

Your body will have to get on with expelling it without help from medicines, which don't work against them.

Recognise that scene? Of course you do. It's becoming the commonest statement that doctors make. It happens so often that people don't really believe it.

Yet most of the time it's perfectly true. Viruses are the underlying cause of a vast number of illnesses.

Take the last few weeks, for example. We had the expected rise in numbers of chest infections due to viruses.

Most people called them flu - but most of them weren't flu in the strict sense at all. Many of them had stuffy noses and very sore throats, with glands in the neck that lasted about six days.

These were winter colds, not flu. They weren't pleasant, but they weren't life-threatening, either. There are around 200 viruses that cause these 'cold' symptoms.

Each time we catch one we get life-long immunity to it - but not to its cousins. That's why most of us catch around 200 colds in our lifetimes.

Another illness that hit Britain in the last two weeks caused sudden vomiting and headache. It seemed to pole-axe people for two to three days, then cleared up miraculously. It, too, was called flu - but the viruses producing it were totally unrelated to influenza.

Their scientific name is enteroviruses, and, like cold viruses, there are hundreds of different forms of them, too.

The only way to treat them is to drink only watery fluids for 24 to 48 hours to give the gut a rest while it tackles the invasion. Lemonade and Cola drinks (the proper stuff containing sugar, not the diet drinks) are a great treatment as they provide the gut lining cells with the right materials to recover faster.

Influenza is a different virus altogether. There are only two main types, the A and B strains.

The current A strain, called the Sydney strain after the city in which it was first found, was the one doing the rounds just after New Year.

'A' influenza hits whole countries hard for around two to three weeks most winters, the peak being the first half of January, then disappears completely. 'B' flu hangs around for longer, picking individuals apparently at random in small outbreaks throughout the whole winter.

They produce exactly the same illness - a chesty cough, muscle pains, exhaustion, fever, misery and feeling dreadful for nearly a fortnight.

For most people they are an inconvenience.

But for people with chronic chest complaints, like bronchitis or heart failure, or people with immune problems, such as after transplants or on long-term steroids or immune suppressant drugs for chronic illnesses (say, kidney disease or blood and bone marrow problems) flu can be the last straw.

It can tip the lungs into failure, or expose them to the risk of pneumonia due to bacteria. That's why they need an annual vaccination against it.

If you are on the doctor's 'at risk' list, then you should make sure you get your 'shot' every October.

Don't wait until January, because by then the vaccine hasn't got the time to work (it takes two weeks to build up your immunity enough to make a difference) and in any case all the doses will have been used up by then.

Converted for the new archive on 30 June 2000. Some images and formatting may have been lost in the conversion.