The Big Question: Is swine flu mutating, and how worried should we be?

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Why are we asking this now?

No parent can have read yesterday's headlines about the death of six-year-old Chloe Buckley from swine flu without a shudder. Teachers described the north London primary schoolgirl as "perfectly healthy" until she fell ill with a virus that her GP initially diagnosed as tonsillitis. Within 48 hours she was dead. Results of a post-mortem examination, which will confirm whether she had any underlying health problem, are awaited. A 64-year-old GP, Michael Day, from Bedfordshire, also died bringing the UK total of deaths to 17.

Does this mean the virus is becoming more severe?

No. The H1N1 swine flu virus is being intensively monitored around the world and there is no sign yet that it is mutating. That is to be expected. There is normally a period after a flu virus emerges when it continues to replicate and spread, before immunity to it grows (among those already infected) and it mutates into something else – which starts the cycle of infection all over again. Experts say that if deaths start occurring in clusters, that could be a warning sign that the virus is mutating into something more serious. For that reason all deaths should be scrutinised.

Why the disparity in people's reactions?

It is one of the many mysteries of flu. Some healthy individuals die each year from seasonal flu, while the majority of the population are only mildly affected, for reasons that are unexplained. Swine flu is so far causing only mild illness in the vast majority of people, but the most seriously affected have been predominantly young. Those with illnesses such as asthma, diabetes, and heart, liver or kidney disease and anyone with a suppressed immune system are more vulnerable. So are pregnant women – the growing foetus pressing on their diaphragm reduces their lung capacity and means if they get a respiratory infection it may be more serious. Obese people are also more vulnerable, possibly for the same reason. Of the UK's 17 deaths so far, at least 14 have been in people with underlying health problems.

Would these people have died anyway?

Probably not. Describing the victims as having underlying health problems conveys the impression that their deaths were unavoidable, even if they had not been infected. This is not the case. A person with asthma is vulnerable to flu because of their impaired lung function. But there is no reason why, if they can avoid the flu, they should not live a normal lifespan.

How many people have been affected in the UK?

The official tally is almost 10,000 cases confirmed by laboratory testing. But tens of thousands more, and probably hundreds of thousands, are estimated to have contracted the virus but not contacted their GP but dosed themselves with paracetamol and hot drinks at home. The Department of Health estimated that new cases were running at 8,000 a week and accelerating, with 100,000 cases a day predicted by the end of August. The age group most affected are children aged five to 14.

Is the death rate higher than for seasonal flu?

It is difficult to tell because there is a tendency in outbreaks of infectious disease to over-diagnose serious cases and deaths and underestimate the numbers infected (who may never contact their GP). Research published in Nature this week suggested that swine flu was nastier than ordinary seasonal flu, causing more lung damage in animals tested. Lung damage can lead to pneumonia, severe illness and death. A study published in Eurosurveillance last week concluded that the death rate was "relatively low... by historical standards". In an average year 4,000 to 12,000 mainly elderly people die from flu, and in an epidemic year that rises to 20,000 to 30,000. In the UK's last major epidemic in 1989-90, around 35,000 people died.

Will we all get swine flu?

No. Some people – the elderly – appear to have immunity against the virus, though it is not yet certain why. Having lived through previous seasonal epidemics and pandemics (in 1957 and 1968) they may have confronted a similar virus before and developed antibodies. Or it may be that the virus happens to have started spreading among younger groups and will reach the elderly later. The most serious illness has been in younger people. Current estimates are that 30 to 50 per cent of the population could be infected – compared with 10 per cent in an average seasonal flu year.

Is it unusual for flu to be spreading in the summer?

Yes. It hasn't happened for decades. Flu is a winter illness. The dampness and humidity in winter help the virus survive longer on surfaces like door handles so it can spread and people tend to mix more closely together in the colder, darker months. But swine flu has found the warm, dry days of summer no impediment, and has spread sooner than experts expected.

Why is the UK worse affected than other countries?

No one is sure. Heathrow is one of the world's major transport hubs, bringing travellers and their viruses from all over the world. The UK also has close links with North America, where swine flu began. The epidemic here may simply be more advanced than elsewhere, and other countries will catch up. Or it may be that we have more sophisticated surveillance systems and are better at tracking the spread of infection.

Is there a vaccine against swine flu?

Not yet, but it is on the way. The Government has ordered 130 million doses, enough to give a double dose – which will be necessary to induce immunity – to the whole population. First supplies are expected by the end of August, and enough vaccine to cover half the population is due by the end of the year. The remainder will be delivered in 2010. The Government will have to decide who is to receive the first doses. Children, the elderly, those with chronic illnesses, pregnant women and NHS frontline staff are likely to head the queue.

Is it a good idea to be vaccinated?

Probably, assuming it is safe and effective. Although swine flu is causing mild illness in most people now, most scientists think it will sooner or later mutate, possibly into a more virulent form. Experience in previous pandemics has shown that novel viruses may start by causing mild illness and end up causing more severe illness, two or even three years on. We could feel the effects of this pandemic for years to come and we don't yet know how severe it may turn out.

What else can we do?

Recognise the symptoms – sudden fever and sudden cough are typical of swine flu. Other symptoms may include headache, tiredness, aches and pains, diarrhoea, sore throat, sneezing, loss of appetite. Stay at home if you are infected and protect the vulnerable in your household by getting antiviral drugs – Tamiflu or Relenza – for them. Use a handkerchief to catch coughs and sneezes, wash your hands – a key transmitter of the virus – and clean surfaces such as door handles. Most people recover in a week, even without anti-viral medication.

Should we be afraid of swine flu?

Yes...

* Although it is causing mostly mild illness now, it could mutate and become more virulent

* It is spreading faster than expected and people with chronic conditions and pregnant women are at risk

* The most serious illness has been in younger people, unlike seasonal flu which is worse in the elderly

No...

* Most people infected with swine flu have suffered nothing worse than a brief fever and a cough

* There is no sign yet that it is mutating, and even if it does it may not cause more serious disease

* With anti-viral drugs and a vaccine on the way we are better prepared than for previous pandemics