At least 17 people have died after contracting swine flu in Britain, while tens of thousands of people are thought to have been infected. Is swine flu getting more dangerous?

No. Laboratory testing around the world indicates the influenza A (H1N1) virus appears to be behaving in the same manner as it was three months ago. The virus is spreading quickly in this country and elsewhere, making it more likely that people will become ill — some of them requiring hospital treatment — especially in the hotspots of London and the West Midlands. The latest studies on animals, published in the journal Nature, suggests that the pandemic strain is more virulent than seasonal flu.

Is there any evidence of the virus mutating?

There have been reports of strains that show signs of resistance to Tamiflu (ostelamivir), the main anti-viral drug used to treat symptoms, in Denmark, Japan and Hong Kong. These are being considered as isolated cases and there is no evidence so far of a drug-resistant strain spreading widely in Britain or elsewhere.

Is it likely to mutate?

Yes. Flu viruses are constantly changing as the emergence of this new swine flu virus — itself a combination of human and animal strains — testifies. There are suggestions that older people may have some residual immunity to the virus as it is similar to H1N1 strains which have circulated in previous decades as seasonal flu.

There may be cause for concern if the virus “reassorts” to become widely unrecognised by the human immune system or resistant to medication, but such changes are more or less random and it is hard to know what form they will take.

It is reported that one in 200 people may die from swine flu. Is this number as scary as it looks?

This calculation is based on a model suggesting that 0.5 per cent of those who suffer from swine flu badly enough to seek medical help may die from it. It does not take into account the fact that the vast majority of cases will be milder infections. Individuals may stay at home for a few days without needing to see a doctor or may not have any symptoms at all after contracting the H1N1 virus.

Researchers from Imperial College London, who produced the figure, say that the one in 200 “case fatality rate” (CFR) is very similar to the estimated number of deaths for seasonal influenza every year. Their research, published in the British Medical Journal, also suggests that the actual CFR in Britain and Europe may be much lower — 0.14 per cent. Due to gaps in swine flu data collection, it is hard to predict how many people will ultimately become ill or die but a surge in cases is expected as the winter flu season approaches.

Why has Britain got the third highest number of confirmed cases in the world?

In the early stage of the outbreak — known as the containment phase — Britain and other countries attempted to confirm every suspected case of swine flu by taking swabs from people with symptoms and sending them off for laboratory confirmation. As of last week Britain had more than 9,700 of these laboratory-confirmed cases, putting it third behind the numbers confirmed in the United States and Mexico, where the H1N1 virus first emerged. But as the number of people reporting symptoms has grown, all three countries have stopped lab tests for all cases to lift pressure on resources. Instead, infection levels are now estimated on the basis of clinical diagnoses.

Britain appears to be the worst affected country in Europe, which may be explained in part by the high rates of travel to and from the US.

There have been calls for a better system of reporting. Is this necessary?

Not necessary, but desirable. There are several different methods of tracking the swine flu virus but officials are now relying mainly on the number of people complaining of “flu-like illness” to their GP.

This weekly data, compiled from a sample of about 100 GP surgeries across the country, is also used to track seasonal flu activity. It may overestimate the total number of people becoming ill if symptoms are not down to swine flu, or underestimate it, if people are not ill enough to contact their GP or treat themselves at home. The Health Protection Agency said last week that of an estimated 27,000 people complaining of flu-like illness in a seven-day period only about 28 per cent — about 8,000 — would be infected with the swine flu virus.

As laboratory confirmation has been discontinued for all but a small sample of cases, experts say it would be useful to have daily updates of the number of people being treated in hospital for flu. Alternatively, wider testing of anonymous blood samples from the general population could also indicate roughly what proportion of people have been exposed to the H1N1 virus.

When will the vaccine be ready?

Ministers suggest that the first batches of a vaccine against the H1N1 flu strain will start being delivered by manufacturers in early September. Following safety checks, they are likely to be in use by the end of that month. The Government expects 60 million doses — enough for at least half the population — to be available this year, with a total of 130 million doses on order.

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