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Flu is everywhere in the media - on TV, radio and online. But is it everywhere in society? Not yet.

Despite all the headlines, it's worth remembering that the rate of flu in England and Wales is still below epidemic levels.

Yesterday, the Chief Medical Officer for England, Sir Liam Donaldson, on the spread of the virus.

I'm grateful to him and to the for permission to use their slides.

First of all, the graph below shows where we stand.

The red line - the current rate of flu - is heading up fast. This is highly unusual in the summer months. The rate of GP consultations last week stood at 155.3 per 100,000 of the population, double the previous week's. It is still below the epidemic threshold of 200 per 100,000. But that masks several hotspots in the UK.

Greater London has half a dozen areas where the rate of consultations is above 400 per 100,000. Not surprisingly, the areas that are more densely populated with higher proportions of children have higher levels of flu. This simply confirms that children are what are known as "super-spreaders" of flu, and you are more likely to get infected if you live in a city than if you are in the countryside.

In the next slide, if you compare the red line - current flu activity - with the last pandemic of 1968-70, you can see that we have a long way to go.

As Sir Liam put it, this is a marathon, not a sprint. It's estimated that 100,000 people got flu in England last week. Put another way, this means that one in 500 got infected - or 499 out of 500 didn't. Infection rates are expected to soar later in the year, as you can see from the historical perspective.

Usually it takes six to 12 months to get an accurate estimate of the number of excess deaths caused by flu. But a rapid confidential investigation has been done by the chief medical officer into the deaths so far in England. As a result, the provisional number of deaths from swine flu in England since the outbreak began remains at 26.

That's a very small number if one wants to start working out percentages with any accuracy, but the next slide shows that 33% of deaths have been in the 0-15 age group and 39% in the 16-44 age group. The over-65 group - normally worst hit by seasonal flu - accounts for 17% of deaths.

Again, I urge caution over the use of the percentages, given that we have had 26 deaths. But given that caveat, you can see that 67% of deaths have been among people with severe underlying health conditions (one example given to us was leukaemia).

Of those who died, 11% had moderate conditions (such as diabetes, controlled by insulin), 6% had mild conditions (such as high blood pressure, controlled by tablets) and 16% had been entirely healthy with no medical conditions.

I have said this many many times, but it is worth repeating: the vast majority who become infected with H1N1 swine flu get a mild illness, and recover completely after a few days bed rest.

Among those who get complications, most recover completely after hospital treatment. While every death is a personal tragedy, fatalities represent a tiny minority of overall cases.

PS: I'm away for a while now - but remember that you can keep up with the latest swine flu news at .

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• - What's this?

There are a lot of anxious people at the Department of Health today. At lunchtime, there will be an important change in the way H1N1 swine flu is managed in England.

(). There will be a unique phone number for people with symptoms to go through an assessment and, where appropriate, to get a unique authorisation number for a course of antivirals.

The focus of the service, however, is online. I've been told by officials that the recommended route for those with internet access will be the website rather than the phone line.

It's the first time that a health service has offered prescription medicine online to anyone who can answer a checklist.

The oseltamivir (Tamiflu) - and the zanamivir (Relenza) for pregnant women - will be free; there will not even be the usual prescription charge. This leap of faith is pretty big.

• Firstly, can members of the public be trusted not to abuse the system by trying to get antivirals when they don't need them? More on that later.

• Secondly, will the website and phone line be able to cope with the demand?

The Department of Health kindly allowed me to access the online system yesterday afternoon before it went live. I should stress that it was a simulation, and I did not end up with any antivirals. But I was able to see exactly how it works.

It is essentially a tick-box symptom checker. The first questions are designed to weed out those who may need urgent medical attention for another condition. Then you are asked to tick a box if you - or the person you are caring for - has a fever plus two or more flu-like symptoms from a list. There are a few other questions designed to weed out those for whom antivirals would not be appropriate.

I went through the online assessment - purely as an exercise - and it took me about three minutes to get a course of antivirals approved. I was given a long, unique authorisation code for a "flu friend" to take to the nearest collection point.

I gave my work address and postcode in Shepherds Bush to find where I could pick up my phantom prescription. Up popped Wormwood Scrubs prison pharmacy, which is helpfully open 24 hours a day - but only, I imagine, for inmates. Oops. I was told that such glitches will have been removed by the time the service goes live.

There will be safeguards to reduce the risk of misuse. You will have to give a name, address and date of birth. Your "flu friend" will have to bring proof of ID for themselves and you. And the system will keep a record of everyone who has used it.

Ministers and officials know that a minority of the "worried well" may try to get antivirals in advance for when they or family members fall ill. Given that some have been paying more than £100 to get drugs privately online, there will surely be some misuse of the system. The question is: how much misuse?

The UK is acknowledged to be one of the best prepared countries for this pandemic. It has enough antivirals stockpiled for half the population, and that will rise to 80% in the future. That means there is more than enough to go round for those who need it.

The online and telephone service is not there for people to stockpile antivirals to take abroad on holiday in case they get ill. And remember that, like all medicines, Tamiflu can have side-effects. The most common is nausea. Most people who get H1N1 swine flu will get over the infection without the need for antivirals. The medical advice is that common painkillers, plenty of fluids and bed rest will be perfectly adequate for most.

So the National Pandemic Flu Service in England is intended for the sick, not for the healthy.

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• - What's this?

The chief medical officer for England, Sir Liam Donaldson, has spoken about the challenges presented by the H1N1 swine flu virus.

Sir Liam has been a pivotal figure in the UK's planning for dealing with a flu pandemic.

A calm and assured voice on radio and television, Sir Liam was responsible for overhauling the government's pandemic planning in recent years, in response to the potential threat from H5N1 avian flu.

Now, faced with the reality of the first pandemic for 40 years, he is spearheading the Department of Health's response to swine flu.

On Thursday - initially in England alone - the National Pandemic Flu Service will take over the assessment of routine swine flu cases from GPs.

There will be a telephone hotline run by call centre staff, most of whom won't be medically trained. But Sir Liam says that should not worry the public.

He said: "That's the case with a lot of health helplines. The staff will be under medical supervision. They will be trained and they will lead people through a set of symptoms."

Is he concerned that people might abuse the telephone and internet assessment process to try to stockpile antivirals like Tamiflu?

He said: "We do have trust in the public. Probably there will be a small number of cases of abuse. People will have a unique number and it will be difficult for people to use it to stockpile Tamiflu for later use."

What about those with underlying health problems who are about to go abroad, perhaps to countries without the same stocks of Tamiflu as the UK - would it be wrong for them to try to get Tamiflu to take with them?

"It would really, the antivirals are needed for people who have symptoms in this country," Sir Liam said.

"The system is not there for people to take it abroad - they need to have good travel insurance or their European health card if they're going to a country in the European Union."

He says dealing with the pandemic "is a marathon, not a sprint" that might involve cancelling some routine procedures.

He adds that if cancellations are necessary to treat those seriously ill from flu in hospital then "that's what will be done".

Is H1N1 swine flu the biggest challenge to the NHS for a generation? Almost certainly yes, says Sir Liam.

"Its 40 years since the last pandemic. There's been no comparable emergency since then. This is a rising tide that will go on for months and months," he said.

You can watch my interview with Sir Liam here.

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• - What's this?

The public health minister Gillian Merron has been in the job just a few weeks, but she might have been expected to have been able to repeat the official guidance to pregnant women on swine flu and crowds.

You can find it in the NHS Choices website. Regarding , it says:

"If you are pregnant, you can reduce your risk of infection by avoiding unnecessary travel and avoiding crowds where possible. Pregnant women should also follow the general hygiene advice."

The key word, which I have put in bold, is "unnecessary". More on that in a moment.

But now to the minister. On the ³ÉÈË¿ìÊÖ News channel Sunday lunchtime, she was asked whether pregnant women should avoid crowds, and had this to say:

"Perhaps I can clarify. We are not advising pregnant women not to travel or not to go into crowds. It's advice if people have swine flu, because as all your viewers will know, the advice, the strong advice if you have swine flu, is to stay at home."

Clarity was perhaps not helped by the Department of Health's decision to "re-state" its advice to pregnant women today - which meant moving it to a more prominent position on .

But this does not contain specific advice on travel and crowds. It never did. So what is the advice to pregnant women?

The answer is to follow the detailed advice on the NHS Choices website. Whatever women decide to do during pregnancy comes down to personal choice.

Let's look at two extremes. Keeping yourself in isolation for nine months - tricky with all those ante-natal checks - is a non-starter. The other extreme would be to go to every rock concert in town and go to as many crowded places as possible. Also not sensible.

The advice on travel and crowds is to follow a common-sense approach. If you have to get a train or bus every day to get to work, then carry on - you should not stop work because of swine flu. Equally, it is sensible to avoid crowds where possible, but this is very difficult if you live in a city.

Pregnant women are at increased risk of complications from swine flu, but the vast majority who get infected will have a mild self-limiting illness. I've dealt with the risks during pregnancy before.

The Royal College of Obstetricians and the Royal College of Midwives have .

Recent news reports have suggested that pregnant women in Australia and New Zealand have been advised to wear masks in public and to stay at home if possible to reduce the risk of swine flu infection.

The latest guidance issued by the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) recommends that "pregnant women should avoid unnecessary exposure to crowded areas, but complete isolation at home would be regarded as extreme for most women".

Experience with the current disease pattern shows that, in most cases, swine flu tends to be a mild respiratory disease. A few cases of severe illnesses among pregnant women and infants have been reported in the UK and other countries (, 17 July). These have mostly affected women with pre-existing health problems.

Current guidance in the UK for pregnant and breastfeeding women remains unchanged. Pregnant women are advised to practice good hand hygiene by washing hands frequently with soap and water. Tissues should be used to cover the mouth and nose when sneezing and coughing, and used tissues should be disposed of promptly.

Pregnant women are advised to avoid crowded places when possible. Women who experience any symptoms of swine flu should contact the National Flu Service (by calling the Swine Flu Information Line on 0800 1 513 513).

Women with symptoms of the influenza who have been advised by the National Flu Service to take antiviral medication should do so. Once the antiviral treatment is authorised, women should arrange for a "flu friend" to collect the prescription on their behalf.

They should follow the advice to stay at home until they become symptom-free. There is currently no evidence to suggest that the use of antiviral medication might cause harm to the baby.

During pregnancy, it is also important to treat fever - a high temperature of about 38C (100F) or more. This can be controlled by taking paracetamol, which is known to be safe in pregnancy.

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• - What's this?

Update 0813, 17 July 2009: This post was updated overnight - it now includes a table and a different explanation of the technical language.

Journalists like numbers. But given a range, the tendency is to go for the extremes. It's just the way we are, I'm afraid.

So given several potential death tolls for the UK from H1N1 swine flu, you can be sure that the headline writers will go for the biggest.

The figure of 65,000 deaths was given in a briefing to reporters by the Chief Medical Officer for England, Sir Liam Donaldson. It's based on what are called "mortality planning assumptions" for the NHS. It's very important to remember that these are not predictions.

What does it mean? Well, the case fatality rate is the percentage of people who may die after getting swine flu (this is a different method of predicting fatalities than that used by Imperial College London - see my previous post, What are the chances of dying from swine flu?).

The clinical attack rate is the percentage of people likely to get swine flu in the population in the first wave - some time between now and the end of winter.

So let's assume, for planning purposes, that 0.1% (one in 1,000) of those who get swine flu, die from it. If 5% of the population get it (the clinical attack rate), that means there would be around 3,100 deaths based on a population of around 60 million. And the other columns give other potential attack rates.

Now, if we take a higher case fatality rate of 0.35% (3.5 people in every 1,000), we get a different set of figures, ending with a potential death toll of 65,000.

You can be sure that this is the one that the headline writers will pick and probably the figure that most people will remember.

The plain fact is that we simply don't know yet how many people will die - but the figure of 65,000 seems extraordinarily high given what's happening around the world and taking into account that number-crunching from Imperial College.

Extreme and unlikely it may be - but it's not impossible, and it was given out by the chief medical officer, so that makes it okay for headlines? Discuss.

While we are dealing with numbers, remember that seasonal flu kills - it's a virus which is much underestimated. The last epidemic, in the winter of 1999-2000, probably caused around 21,000 excess deaths, and in an average winter, flu may kill 6,000 people.

The real difference we note when comparing pandemic to seasonal flu is the groups targeted. The biggest group who die from seasonal winter flu is made up of the frail elderly. They are least likely to catch H1N1 swine flu - but if they do, they have a greater than average risk of complications.

For some, it's when they read about young adults dying with swine flu and children in hospital that they begin to get really worried. It is a time for concern, especially for those with underlying health conditions (for a list of these, see posts from 12 June and 26 June). It's also a time in which we should all take personal hygiene seriously: .

There will be some deaths among people who were previously entirely healthy. But we can get a different perspective if we compare that to other risks we run each day, like , which kill around 3,000 people each year, or .

The vast majority who get H1N1 swine flu will be fine - and many won't realise that they've had it.

A lot will feel lousy for a few days. A minority will have complications and some will die. That is the reality of infectious disease. We are better prepared than ever to fight this pandemic. Antivirals like Oseltamivir (currently best known as the brand name Tamiflu) are effective, and a vaccine is coming - though it will be touch-and-go whether most at-risk groups are immunised before the peak of the first wave of infection.

PS: The Department of Health website has published and the Health Protection Agency its .

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• - What's this?

The recent deaths of people with H1N1 swine flu especially that of a six-year-old girl in London, has led many to perceive that the virus may be getting more deadly. NHS Direct say the number of calls they've received on swine flu has increased by 50% to 9,000 a day.

The reality is that there are no indications that the virus is mutating or getting more virulent. Laboratory testing around the world indicates the H1N1 virus appears to be behaving in the same manner that it was three months ago.

The rise in the death rate is due to the huge increase in the number of cases. Even seasonal flu can, rarely, kill young children. Every winter, flu contributes to thousands of deaths, mostly of the frail elderly. The difference with H1N1 swine flu is that it is tending to affect those under 65.

Many people want to know what their chances are of dying from the virus. The simple answer is that it's very, very low. The UK has probably had tens of thousands of cases (we don't know how many - more on this in a moment) and there have been 17 deaths.

Researchers at Imperial College London have warned that accurate predictions about the death rate are not yet possible.

The researchers say the best estimate so far is that about 0.5% of those who get swine flu bad enough to seek medical help may die from it. This is what they call the case fatality rate.

Professor Azra Ghani, an epidemiologist at Imperial, explained that this could be very wide of the mark:

"Our best estimate, based on the cases that come to the health system is around 1 in 200 (deaths) at a maxiumum which is very similar to the estimate you would see for seasonal influenza but that doesn't take into account many of those milder infections where individuals may stay off for a few days or not display any symptoms at all."

It's worth reiterating that this case fatality rate doesn't include a huge group - people who get sick and never seek medical help, nor those who get infected but are without symptoms.

If there is a sudden surge in the numbers seeking medical help because they perceive the virus is more dangerous, it would change the case fatality rate.

The researchers also point out that some deaths where swine flu was a contributory factor may be missed because it is not always tested for.

They want more accurate mapping of the actual numbers getting the virus. This would involve community testing of representative households and combining this with hospital reports of sickness.

For those of you who like the raw data, I'm attaching one of the tables presented by the disease mappers at Imperial. I'm indebted to them and to the British Medical Journal for permission to reproduce it here. The crude and adjusted case fatality ratios show that estimates in the worst affected countries vary very widely.

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• - What's this?

The World Health Organisation has said that healthcare workers should get priority access to vaccination against H1N1 swine flu.

Dr Marie-Paule Kieny, WHO director of the , reiterated the message that the virus was "unstoppable" and all countries would need access to a vaccine.

She said healthcare workers should be the main priority group for vaccination, to protect them from the risk of infection, and to ensure they could continue to treat patients with a range of illnesses.

Her comments came as news emerged of .

Dr Michael Day, a GP, died on Saturday in the Luton and Dunstable Hospital. A swab test showed that he had the virus, but the exact cause of death has yet to be established.

Paying tribute to Dr Day, the chief medical officer for England, Sir Liam Donaldson said: "It is a very sad case. He was a very dedicated doctor, loved by his patients."

He added, " It won't be much more than a relatively mild illness for most people and not everyone will get it in the first wave of attacks. In past experience of pandemics its been no more than 30-35% of the population and then in succeeding flu seasons others get it". He said this made vaccination very important.

Dr Day's death, together with that of a six-year-old girl brings to 17 the number of fatalities linked to the virus in the UK. Chloe Buckley, from north west London died on Thursday. A post-mortem examination will be carried out to determine if she had any underlying health conditions.

Dr Marie-Paule Kieny, presented feedback from a meeting on 7 July of SAGE, , who advise the WHO and member states.

She added that, in no particular order, other priority groups for vaccination would be pregnant women, anyone over six months with chronic health conditions such as respiratory problems, healthy adults under the age of 49, healthy children and healthy elderly people. Clearly this includes whole populations so governments will have to decide which groups to protect first.

Dr Kieny said that obesity had been noted as a risk factor but experts are unsure whether it is obesity itself or the health conditions that arise from it. People with a BMI (body mass index) of over 30 and especially over 40 had been noted as having a higher chance of severe disease.

Problems with vaccine yield

Dr Kieny said vaccine yields had so far been poor but manufacturers were looking at alternative strains which might increase output. Most flu vaccines are grown in eggs and it seems that H1N1 swine flu is producing less yield than other seasonal flu strains.

"Some strains are good yielders and some are bad," said Dr Kieny.

"It is not a severe problem yet," she added, as the production is enough to do the clinical trials needed to test the vaccine and other, better yielding strains may emerge. These will be generated from the WHO laboratory networks around the world having isolated samples from patients with the virus.

So Dr Kieny sounded a note of reassurance, but if the low yield continues, then it would spell problems for the amount of vaccine that could be produced.

Analysis of H1N1 virus

I'd also like to draw your attention to , analysing the H1N1 virus.

Yoshihiro Kawaoka of the University of Wisconsin, who led the study found that the virus showed a greater ability to infect that lungs than seasonal flu viruses. Tests in animals confirmed studies that show the swine flu strain can spread beyond the upper respiratory tract and go deeper into the lungs, makng it more likely to cause pneumonia.

Commenting on the paper Professor Ian Jones, Director of Research, University of Reading, said:

"This complete analysis of the current H1N1 is what we've been waiting for. For a number of measures it shows that the new virus is more serious than seasonal H1N1 but that, nonetheless, the major outcome to infection is recovery. For the few cases of severe infection, the data should help in the clinical management of hospitalised patients.

Wendy Barclay, chair in influenza virology at Imperial college London, said:

"This is an absolutely solid piece of thorough research that confirms and extends what was published in Science Express last week. By comparison with a seasonal human H1N1 virus, it is shown that the swine origin H1N1 infect cells deeper into the respiratory tract. It must be borne in mind that typical circulating human strains of H1N1 have been associated with rather mild illness in recent years, and that the swine origin H1N1 may be behaving in these animal models more alike the type of H3N2 viruses that caused a pandemic in 1968."

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• - What's this?

Several people have been commenting about an apparent lack of information on H1N1 swine flu. Suggestions have been made that the "real" situation is being covered up.

That has never been the case in my opinion, and this post should provide a wealth of material for those who want it.

I'm grateful to the chief medical officer for England, Sir Liam Donaldson, for allowing me to post up data and images from the technical briefing he has given to journalists.

From now on, there will be a weekly situation report from the Department of Health on the situation in England with separate reports from Wales, Scotland and Northern Ireland.

Which brings me to Sir Liam's presentation.

Tracking data

This pyramid shows what information will be released each week.

First, there is the number of deaths (a total of 14 in the UK so far), then the number of hospitalisations that week, the level of antiviral use and the percentage remaining stocks of Tamiflu and Relenza, and finally the total number of cases from GP consultations and contact with NHS Direct or the National Pandemic Flu Service (when it is up and running).

The swine flu iceberg

This is a good visual way of showing what happens during a flu pandemic. At the top of the iceberg, above the water, you have people with H1N1 who seek help from the NHS, but another group below the water who have the virus but cope okay at home. Then, below the dotted line, the majority of the population who are healthy and unaffected.

What we don't know is how many of us will fall into each category or when the outbreak will peak. In the last flu pandemic of 1968-70, the UK had a comparatively small outbreak in the first winter, with a much bigger case load the second winter.

Royal College of General Practioners

GPs have a long-standing and well-organised system for monitoring the spread of influenza-type illnesses.

Clearly, they can't and don't swab everyone who comes to them or calls them with symptoms of flu. So instead the RCGP has what's called "spotter" practices who make detailed reports about the sort of symptoms they are seeing. From this, national figures are scaled up.

This graph may look daunting, but please persevere. First, let me draw your attention to the two horizontal dotted lines. The lower one is the baseline threshold for flu. This figure is 30 consultations per week per 100,000 people.

The rate is it regarded as significant only when it goes above this. Then there's the epidemic activity line of 200 consultations per 100,000 people.

You can see from the brown dotted line (the big peak) that the last epidemic of flu in England was in the winter of 1999-2000.

Now look at the red line which is 2008-present day. Trace it back to week 52 (the end of December 2008), and you can see that last winter was not a very bad one for flu.

Trace the line forward and you can see the current red line is heading skywards. It equates to 51.9 weekly consultations per 100,000 people for the week ending 5 July. Sir Liam said that this equated - very roughly - to about 27,000 consultations a week.

Of course, not all of those contacting their doctor will have swine flu. The latest estimate is that 28% - or 3 in 10 - will have the virus. The rest will have a bad cold or some other bug.

RCGP consultations by SHA

This graph gives a breakdown of the previous figures by Strategic Health Authority; it shows that the virus has hit some areas of England far more than others.

The black line shows that flu has reached near-epidemic levels in London, while the red dotted line shows a significant level of activity in the west Midlands. But north-east England is still largely unaffected. As the autumn progresses, we should expect all areas to have significant levels of flu.

Comparing data sources

This is an important graph as it shows a good correlation between the number of confirmed new cases from lab reports (the blue line) and the weekly caseload from the RCGP "spotter" practices.

If these two lines were widely divergent, it would suggest that there was something wrong with the data collection.

Hospitalisations

This is a snapshot of the number of people in hospital with suspected H1N1 swine flu in England as at 8am on 8 July. You can see that children under five and those aged five to 15 represent two large groups, but there are also lots of cases in the 16-64 group.

Comparatively few hospitalisations are occurring in the over-65s, who make up the group most affected by seasonal flu. In all, there were 335 people in hospital and 43 in critical care. There have been 14 deaths where swine flu is the cause or the suspected cause.

Apologies to those in Wales, Scotland and Northern Ireland that I can't give you a separate set of data. I would like to have all the material UK-wide, but the Department of Health says there is such an enormous amount of data that it would be impossible. But the Health Protection Agency will give out UK figures on lab-confirmed cases and deaths.

To sum up, this will track the size and spread of H1N1 swine flu in the UK, what the global trends are, whether the virus is mutating or becoming drug-resistant, what level of pressure the NHS is under and the uptake levels for flu vaccine.

The official number of laboratory-confirmed cases in the UK was 9,718 as of yesterday. But this figure is not really worth considering any more, because the vast majority of people are not tested for flu.

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• - What's this?

There is a lot of hope and expectation resting on a vaccine for H1N1 swine flu. Global vaccine manufacturers have received the seed virus and are growing this to produce doses for clinical trials.

One key player will be . It has around 45% flu vaccine market worldwide.

Company spokesman Dr Albert Garcia explained that last year the company produced 170 million doses of seasonal flu vaccine, with around 130 million doses for northern and 40 million doses for southern hemisphere.

I wrote last week about Novartis and Baxter, who are both producing some flu vaccine using cell culture. But Sanofi Pasteur relies wholly on the slower and seemingly outdated process of growing the vaccine in fertilized chicken eggs. Why?

"We find egg-based technology is the most reliable method for producing flu vaccines in bulk" said Dr Garcia. "It is very robust." In other words, if something is not broke, why try to fix it?

Flu vaccines have been created successfully for decades using eggs. Cell culture production is much more recent and is still an emerging technology which has experienced teething problems. But it is several weeks, even months faster, important in a pandemic.

So how much vaccine might be available? By my reckoning, it takes three eggs to produce a trivalent seasonal flu jab - one egg per strain of flu. So does that mean the company can produce not 170 million doses in the coming twelve months, but 510 million?

Dr Garcia said: "It's not so simple". He explained:

"We don't know what the yield of H1N1 vaccine will be, nor do we now how many micrograms of vaccine will be needed in each dose. The aim will be to produce as many doses as possible in order to protect the maximum number of people. But it all depends on the outcome of the clinical trials."

It's also not clear whether people will require one or two jabs. Against seasonal flu one vaccine is given each autumn, but it's been presumed that two doses will be required to give protection against a pandemic strain.

Sanofi Pasteur is one of the few manufacturers producing seasonal doses for the southern hemisphere ().

So what will happen to this autumn's production - due to start in October - of next year's doses of seasonal flu vaccine, due to be distributed in spring 2010?

Interestingly, it seems the WHO has not yet made a decision about whether to sacrifice this production by asking SP and CSL to switch entirely to making H1N1 swine flu.

"We are at the disposal of the WHO" says Dr Garcia. "We have not had a request to switch totally to H1N1 pandemic vaccine."

That decision doesn't need to be taken yet, until clinical trials of the H1N1 vaccine have been completed. But by September, someone will have to decide whether to abandon seasonal flu vaccine for the time being, and concentrate on swine flu.

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• - What's this?

A lot of people have asked who will be the first to get immunised against H1N1 swine flu.

gives a long list of priority groups.

But it's not clear whether the list is in descending order of priority; it is all rather vague. Some GP surgeries, I'm told, are seeking clarification. See if you can work what it all means from this section:

It's interesting that poultry workers but not pig farmers are mentioned. And there's another bit of confusion that I'm hearing about. Some NHS staff apparently thought that the H1N1 immunisation programme would be instead of - rather than in addition to - the regular seasonal flu campaign. It's not.

There's a very important public health message here for the NHS and for the public. Vaccination against seasonal flu this autumn will continue as normal. H1N1 swine flu vaccination is an add-on.

That means a lot of work for immunisation teams. They will have their regular at-risk groups and the over 65s for seasonal flu. They will also be giving H1N1 swine flu vaccine to at-risk groups, but not (initially) to the elderly.

Is there scope for confusion this autumn? You bet.

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• - What's this?

A lot of people got quite a shock yesterday when Andy Burnham, the health secretary, .

And then on Newsnight, the chief medical officer for England, Sir Liam Donaldson was asked whether that meant that 40 people a day might be dying from swine flu:

"Well we can't be sure about the death rate, nor can we be absolutely sure about the number of cases that will be occurring by the end of August. But these are scientific projections, the numbers could be lower than that, they may be even higher.'"

So there you have it. Predictions, projections, but not facts. The only facts we have are that there have been around 7,500 lab-confirmed cases of swine flu (thousands more unconfirmed) and three deaths. That makes a death rate of one per 2,500 cases or 40 per 100,000.

Could the 40 deaths a day figure be accurate? The US experience may help us. They are about one month ahead with swine flu and the CDC reckons (here comes another estimate) that at least one million Americans have had swine flu. They made that prediction when there had been 127 deaths in the US. So, using the American figures, that would give us a UK death rate of one per 7,800 cases or 12 deaths a day come the end of August.

Which goes to show that predicting death rates, and even case numbers, is an inexact science, and such predictions should come with a health warning.

One figure which people should not be surprised by is the number of cases. One hundred thousand a day seems perfectly possible at the peak of a national epidemic. The real surprise will be if it comes in August, even before children return to school.

This large "attack rate" of a pandemic virus is to be expected when so many are exposed to a new virus. The predicted (oops, there we go again) that 25% of the population might get infected. That's 15 million people.

The infection will probably come in a few waves spread over about two years. A daily rate of 100,000 infections would take you to 10 million people in 100 days. I'm not predicting that, just doing the maths. I certainly think it's too early to predict eventual death rates with any certainty.

What no-one has quite worked out yet is the number of people who are asymptomatic - that is, they have the virus in their system but show no (or few) signs of ill-health. This rate must be pretty high and it helps explain why the disease is spreading so quickly, because symptomless people are less careful when mixing with others. It's another reason why basic hygiene is crucial.

Let's stick then with what we do know. The majority of people so far infected have had a mild illness and recovered completely without the help of antiviral medicines. Some with swine flu will simply feel a bit grotty for a few days. For very many, uncomplicated swine flu will still be - laid low in bed with a sudden fever and cough.

Add to that a selection of the following: headache, aching limbs, lethargy, joint pain, diarrhoea, stomach upset, chills - I could go on. That still classifies as a mild illness, because after a few days in bed feeling awful, you get over it. Those with underlying health conditions and pregnant women are certainly at greater risk but they too should not be unduly alarmed, but vigilant for the symptoms.

And once again, as per medical advice, please turn down any invitations to swine flu parties (do they really exist?). It does not pay to expose yourself to this virus about which much is still unknown, and you could spread it to others who are less robust. Remember that about a quarter of the deaths so far in the US have been among people who had no health problems. I would prefer not to risk my health, but hold tight for the vaccine.

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I've been on a flying visit to Marburg, Germany to look round the cell culture manufacturing plant of Novartis.

Vaccines are important because they are the only way to ensure protection from the H1N1 swine flu virus - short of moving to an uninhabited island.

Two weeks ago , weeks ahead of expectations.

You can see from the photo that I held the jab in my hands. Just one small point - on the label it says "not for human use". So what's happening?

Novartis created the vaccine from the wild type strain of H1N1 - the sort people are catching every day. But it's a slightly modified reassortant seed that flu manufacturers are all using for their pandemic vaccine.

Novartis has demonstrated impressive speed in production, creating the experimental vaccine in just six weeks. It shows the huge advantage of growing flu vaccines in cells rather than eggs, where production takes several months.

But the race to create a vaccine won't surely have been won until the first batch of vaccine is delivered.

Novartis is just a couple of weeks behind with the first doses using the reassortant seed, so they may well still be the first to produce bulk doses. Before that happens, there will have to be clinical trials which will take a couple of months, and the product will have to be licensed.

Novartis has certainly proved itself to be the most media-savvy of the pharmaceutical companies in promoting its pandemic vaccine.

Standing in front of the steel tanks in which the vaccine will be produced, Novartis executives said they hoped to make 500-600 million doses of pandemic vaccine with a price tag of between $10-15 per jab.

In line with other manufacturers, the cost will be less to developing nations. Novartis made it clear that they would not be "giving away" any doses.

This is in contrast to one of its rivals. Two weeks ago the of 100 million doses of H1N1 vaccine from Sanofi-aventis, which is the world's largest flu vaccine manufacturer.

It was impressive to see the CEO of Novartis Vaccines, Dr Andrin Oswald, give interviews in fluent German, English and French. You can watch my interview with him below.

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The Health Secretary Andy Burnham is giving a statement to the Commons later today at which I understand he'll signal a new phase in how H1N1 swine flu is dealt with.

I understand that a move to the so-called "treatment phase" will happen very soon. This will be a UK-wide policy and will unify the approach of the health service in tackling the disease.

At present, there is a flexible approach: GPs in hot-spot areas like London and the West Midlands have stopped swabbing every person who reports swine flu smptoms.

The changes are being made to relieve the pressure on health officials. Those who contact NHS Direct with uncomplicated symptoms will be told to stay at home while arrangements are made for them to get Tamiflu.

This has always been the case, but the need for testing has meant that many have seen either a GP or other health official to confirm the diagnosis.

People who have come into close contact with those infected will no longer be chased up and offered drugs.

This policy will soon be extended UK-wide. I don't have the precise timing, but am told it will be soon.

I should stress that this is NOT a sign that the virus is getting more virulent. It IS an admission that the spread of the virus can no longer be contained. Those who have symptoms will still be offered Tamiflu, although this might eventually be restricted to those most at risk - people with lung, circulation and immune disorders.

For more information on what the treatment phase involves, see a post from last week ("Radical use in antiviral use considered").

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