Experts have warned that a major influenza epidemic is on the way. And far from being a benign illness, says Roger Dobson, it can be fatal. So what can you do to protect yourself?

"The patients were short of breath, and after gasping for several hours, they became delirious and incontinent, and many of them died struggling to clear their airways of a blood-tinged froth that gushed from their nose and mouth.''

"The patients were short of breath, and after gasping for several hours, they became delirious and incontinent, and many of them died struggling to clear their airways of a blood-tinged froth that gushed from their nose and mouth.''

That was how one young doctor reported the symptoms of patients admitted to hospital in 1918 suffering with what many at the time thought was a respiratory disease caused by bacteria.

What the patients actually had was influenza, and a devastating strain of the disease that was to go on to kill 20 to 30 million people worldwide in 1918 in the biggest epidemic since the Black Death. There has never been such an epidemic since, and although there have been a number of smaller outbreaks, recent years have seen a decline in reported cases. As a result of that drop in numbers, and the arrival of the flu vaccine, fears and concerns about the disease have declined, too. Flu is often seen now as being no more serious than a bad cold.

But unlike the common cold, flu can cause severe illness and life-threatening complications in many of its victims, especially the vulnerable, such as the elderly, the very young and the infirm. Symptoms include fever, headache, extreme tiredness, dry cough, sore throat, runny or stuffy nose, and muscle aches. Children in particular can have additional symptoms including nausea, vomiting, and ear infections. Complications triggered by flu include bacterial pneumonia, dehydration, and a worsening of chronic conditions such as heart failure, asthma and diabetes. It is estimated that, in an average year, there are around 4,000 deaths due to flu, but in a bad year that can rise to more than 20,000.

One of the obstacles to getting to grips with flu is that the virus is constantly changing and evolving. Vaccines only protect against specific strains, and every so often, the virus mutates significantly to form an altogether different, and nastier version. Six years ago, the discovery of so-called "bird flu" in Hong Kong sent shock waves around the world because of the high death rate - six deaths out of 18 reported cases - but no further cases have been reported of the AH5N1 virus in humans.

But another new strain from Asia has now been recorded, and has been implicated in the deaths of half a dozen children in Britain. And after several quiet years, the number of flu cases is rising. Indeed, experts have just warned doctors to prepare for a major outbreak of this flu that could affect more than six million people nationwide.

"For the last three years, we have seen very low levels of flu in the UK, but flu activity has started earlier than normal this year, so we are expecting to see more cases. Children and adolescents have been particularly affected, and there have unfortunately been a few deaths due to flu reported in children in England over recent months," says Dr John Watson, a respiratory expert at the Health Protection Agency, which is urging people to be alert to symptoms of flu and is encouraging at-risk groups, including the over-65s, to make sure that they get their flu vaccinations.

Laboratory testing has identified the main bug circulating as AH3N2, a Fujian-like strain that is different to the AH3N2 Panama-like virus that has been circulating in the UK over the last few years, and which is in the current flu vaccine.

The virus is thought to have originated in the Chinese province of Fujian, from where it moved to Australia, where it was responsible for the biggest flu outbreak for five years. It has since been reported in Argentina and Chile, as well as in the UK.

One of the main problems that arise when flu viruses mutate is that they are more likely to affect the young who will have less immunity to them, and the vulnerable who will have less resistance. The very young, whose immune systems are still developing, may be particularly at risk, and the latest advice is that children over six months who fall into the at-risk group should be vaccinated. Flu vaccination is also recommended for people with a chronic heart or chest complaint, including severe asthma, as well as people with chronic kidney disease, diabetes, or lowered immunity.

But what else can you do to protect yourself from infection? Good hygiene is another way of reducing the risk. Flu is highly infectious and can be spread by breathing the same air as someone with the disease, or by touching them, or by coming into contact with things that they have touched. There is evidence that the virus can exist for some time on work surfaces or towels, from where it can get on to hands, and from there to noses and mouths. Good anti-flu hygiene includes washing dishes at a high temperature, wiping surfaces regularly after use, and washing hands frequently.

Keeping away from people who have flu in the early stages of the infection can also lower the risk of infection. The period when an infected person is contagious depends on the age of the person. Adults may be contagious from one day prior to becoming sick, and for three to seven days after they first develop symptoms. Some children may be contagious for longer than a week.

Although there is no cure for flu, some drugs do reduce symptoms, especially if taken within two days of the start of the illness. They are designed to reduce the duration of the disease, and trials suggest that they cut one or two days off its lifespan. Starting the drugs early is important, but a problem here is that many people do not know that they have been infected for some time. It takes between one and four days from the time of infection for the first symptoms to appear. Decongestants and cough suppressants may relieve some cold symptoms but they will not prevent, cure, or shorten the illness, and they sometimes have side effects, including drowsiness, dizziness, insomnia, and an upset stomach. Antihistamines may relieve symptoms such as a runny nose and watery eyes.

Many are convinced that taking large quantities of vitamin C will prevent flu or relieve symptoms, but several studies have failed to find any conclusive data to support the idea, although the vitamin may reduce the severity or duration of symptoms. A test on schoolchildren found that those taking daily supplements of vitamin A had 22 per cent fewer bouts of flu.

General advice for generally healthy people who suspect that they have flu is not to visit their GP, because of the risk of spreading the virus to more vulnerable people, and to stay at home rather than passing the bug on to work colleagues or schoolmates, and to drink lots of fluids. The goods news is that for most people, the worst is over after seven days.

The bad news is that some strategists have been predicting that, statistically at least, the world is due another big outbreak of influenza. Not on the scale of the Spanish flu of 1918, which actually started in America rather than Spain, but severe enough to kill several thousand people.

More bad news is that the biological- weapons scientists are concerned that terrorists may harness the flu strain as a weapon of war. "Even if a lethal human influenza virus does not emerge in nature, it is likely that it can be generated in the laboratory. A virus would be a major challenge, and would require strategies similar to those used to thwart a bioterrorist attack,'' says Dr Robert M Krug, a molecular geneticist at the University of Texas.

"It can be argued that most terrorists would not have the knowledge, facilities and ingenuity to carry out these recombinant-DNA experiments. This is probably the case at the present time, but the situation can be expected to change in the future, perhaps after as little as five to 10 years.''