Influenza viruses have been causing sickness for thousands of years so it may seem curious that there is still a huge amount that we don't understand about them.

This applies especially to H1N1 swine flu which, admittedly, has only been circulating in humans for a matter of months.

A series of research projects in the UK have been announced which will examine every aspect of the swine flu virus - in pig and human populations, and in hospital intensive care units.

£7.5 million pounds of funding has been given by the Medical Research Council (MRC), Wellcome Trust, and Biotechnology and Biological Sciences Research Council (BBSRC) along with some government support.

The research will aim to answer many of the questions which posters on this blog have raised, and more besides:

• Why do some people and not others become seriously ill with swine flu?
• What proportion of people who are infected have no symptoms (what's known as asymptomatic)?
• If you are asymptomatic, can you still spread flu?
• How useful are antivirals?
• How effective is the vaccine?
• How does H1N1 swine flu behave in pigs?
• Is there a risk that the virus could evolve into a more virulent form in pigs?
• Is there a need for a vaccine for pigs to slow the spread of the virus?

Fluwatch

A study led by Dr Andrew Hayward of University College London, which will follow up to 10,000 people and look at the duration and severity of symptoms, their access to treatment, use of antivirals and uptake of the vaccine.

We should not have to wait long for results. Dr Hayward said he hoped to release initial data before Christmas.

This study should help scientists work out what proportion of the population has had swine flu. This is crucial because at present we have only tenuous estimates from the Health Protection Agency which are subject to a huge margin of error.

Last week's estimated cumulative number of cases was 620,000 in England (with a range from 289,000 to 1,278,000).

The reason we don't have a clear idea of how many people are infected is because the majority of those who get flu, never go anywhere near the health service and only the sickest patients get tested for the virus.

If we knew what proportion had no symptoms or recovered without bothering their doctor, it would help us understand how quickly we may get through this pandemic.

It will also look at how effective antivirals have been in treating flu - a hot topic for months. Some have criticised the policy here of offering Tamiflu to anyone who says they have flu-like symptoms.

Dr Fred Hayden from the Wellcome Trust (Professor of Medicine at the University of Virginia) pointed to a study in the New England Journal of Medicine last month. This looked at nearly 300 patients admitted to hospital in the United States.

Dr Hayden said:

"[F]or those admitted to hospital, the average time they waited before getting antivirals was three days, for those admitted to intensive care it was six days and for those who died it was eight days."

He said that early treatment, even in uncomplicated seasonal flu, could reduce the risk of complications.

The Mechanisms of Severe Acute Influenza Consortium (MOSAIC)

Thankfully the principal investigator, Professor Peter Openshaw from Imperial College London, came up with the snappy acronym MOSAIC.

A team of scientists from England and Scotland will look at up to 500 people hospitalised with flu during the pandemic and try to find out what factors contributed to the severity of their disease.

For example, was there something about their genetic make-up which made them more susceptible to the virus, or was it due to variations in the virus itself?

They'll be taking around 40 samples from each volunteer and doing extensive virology and bacterial work in several UK labs.

This study will take about a year to complete and, like the others, could yield useful information for future pandemics.

Combating Swine Influenza (COSI) Initiative

There are two studies here looking at the evolution and spread of pandemic H1N1 virus in pigs and how to develop ways to slow the spread of the virus in animals and humans.

The research will be led by Professor James Wood at the University of Cambridge and Professor Ian Brown at the Veterinary Laboratories agency at Weybridge.

Professor Wood said that for the last 10 years scientists had concentrated more on avian influenza and there was a lack of detailed surveillance in pigs.

"It's important we understand the evolution of the H1N1 pandemic" he said. "We need to look at where it came from and how it's evolving. It's possible that it may take a different evolutionary course in pigs and pose a different threat to humans."

He pointed out that farmers had passed the H1N1 pandemic virus to pigs in Argentina, Australia, the USA and Canada.

One issue that has been puzzling me is why the pandemic virus is currently so stable. We are always told that RNA viruses like flu have a high mutation rate. It's why people need a flu jab each autumn.

Professor Wendy Barclay, virologist at Imperial College London said there was genuine uncertainty about the H1N1 swine flu virus: "We don't know why it's so stable" she said.

Nonetheless, she had a theory:

"It currently has a huge number of hosts (people) to infect and so has no pressure to mutate. But as more people develop immunity it will have to work a lot harder and so we will expect to see drift (mutations) which might be accompanied by changes in its virulence."

That might of course mean that swine flu has a sting in its tail. "Pandemic, what pandemic?" has been the refrain from some journalistic colleagues recently. And it's true that the first pandemic of the 21st Century is a viral pushover for the vast majority of us.

But for a small minority it is a serious threat, hospitalising hundreds of Britons each week, a good proportion of whom have no underlying health problems.

The sooner we know why flu is able to breech the defences of some people and not others, the sooner we might be able to develop better ways to beat the virus.

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A few words about how the H1N1 virus is progressing on its relentless attempt to reach every corner of the globe.

New figures from the World Health Organization show the virus has now spread to more than 199 countries and territories and that there have been more than 6,000 deaths.

Although every death is a tragedy, that is a remarkably small number given that seasonal flu is reckoned to contribute to the deaths of at least 250,000 people per year. It is yet further evidence of the generally mild nature of the virus.

Having said that, swine flu has a sting in its tail.

Australia, like several other southern hemisphere countries, has recently emerged from its winter flu season.

Deaths were low compared to seasonal flu, but hospital intensive care units had not seen anything like it in 40 years; indeed, since the pandemic of 1968-70.

It sums up the apparent contradiction about this pandemic: mild for most, but very serious for a small minority.

Those at greatest risk of complications are pregnant women and anyone with an existing health condition such as asthma. That's why these groups are being immunised first.

Unlike seasonal flu, which tends to kill the frail elderly, the average age of those who've died from the virus here in the UK is 44. One in five of those who have died had no previous health problems.

As I have said before, swine flu should not be a reason to panic - nor is it something to dismiss out of hand. We can all do our bit to minimise the spread of the virus by following good respiratory and hand hygiene.

Several of you have asked about what's happening in Ukraine which, in just a few weeks, has recorded more than 250,000 cases of flu-like illness, with 235 people needing intensive care and 70 deaths.

As far as I can make out, there does not seem to be anything unusual about the outbreak there. One health official said it was probably a reflection of the poor state of the health service that the virus had had such an intense effect.

Crucially, samples of the virus have shown that it is not mutating, so is the same H1N1 pandemic strain that is circulating worldwide. As long as that remains the case, we should feel reassured.

Finally, if the virus has spread to 199 countries and territories, does anyone know where on the planet has not experienced swine flu?

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It is curious that although the overall number of H1N1 swine flu cases has been fairly static over the past week, intensive care units continue to come under increasing pressure. The Chief Medical Officer for England, Sir Liam Donaldson, gave his weekly update to journalists via video link from Washington, where he's attending health meetings.

Sir Liam said: "there has been a snowballing of cases in intensive care units in recent weeks which is giving us real concern". He stressed that there was no evidence that the H1N1 virus was mutating. "It is unexplained," he said, adding that he'd met the chief medical officer for New Zealand in recent days who had pointed out that his country had seen a similar phenomenon over their winter. Half-way through their recent flu season there had been a fall in the severity of most cases in the community but an increase in severity in a minority of cases with complications.

My thanks to the Department of Health, as always, for providing this data for the blog. Never before has a pandemic been so closely monitored, in real time. This chart shows that as of 0800 on 4 November there were 848 people of all ages in hospital in England with suspected swine flu. Of these, 172 were in critical care. Last week there were 751 in hospital of whom 157 were in intensive care.

That seems surprising when you look at what's happening to swine flu from weekly consultations with GPs.



This is a key graph for understanding what the H1N1 virus is doing. As always, look at the solid red line. You'll see that it actually dipped a bit in the week up to 1 November. Health officials think this is probably the result of children being on half-term, rather than the start of a downward trend.

The Health Protection Agency estimates there was a slight increase in cases of swine flu in England this week, to 84,000 cases, up from 78,000 the week before. Remember though there is a huge margin for error because very few people are tested for the virus and we still don't know the proportion of those who get infected yet have such a mild illness that they either don't know they've had swine flu, or they cope without bothering the health service.



This is a useful chart because it shows, by age group, the ratio of people in the community who have been hospitalised. Children under five represent the biggest group needing hospital treatment. If you look at the five to 15 age range, this is the only group where there was a fall in the ratio hospitalised over the past week (probably due to half-term).

Vaccine

I promised to update you on how the distribution of swine flu is going. Health officials confirmed that 6.4 million doses of the GSK vaccine Pandemrix were now in the UK and of these, 4.4 million had been distributed. Sir Liam said that by the end of next week virtually all GPs would have received their first delivery of swine flu vaccine. The warehousing and distribution of the vaccine is being handled by Movianto, which on its website says that it delivers 40% of all domestic pharmaceutical products in the UK.

Movianto also has 1.43 million doses of Celvapan, the swine flu vaccine made by Baxter. This is being reserved for the tiny proportion of people who have a severe egg allergy as (unlike Pandemrix) it is not grown in eggs. The potential downside of Celvapan is that two doses are required to confer immunity compared to one dose of Pandemrix, which explains why the GSK vaccine is the one primarily recommended by the Department of Health.

A reminder that vaccination against the H1N1 pandemic strain is being limited, initially, to people considered most at risk of complications of flu (such as those with asthma, heart disease or immune disorders).

In addition, front-line health workers are being immunised. There are no figures yet on uptake of the jab among NHS staff, but Ian Dalton, the NHS flu resilience director, said that anecdotal evidence was looking good: "It's very positive," he said. "There's a sense that staff recognise it will protect them, their families and patients."

Extending vaccination

As I've said before, it's just a question of time before the swine flu immunisation programme is extended beyond at-risk groups, with healthy children being the next priority.

The Conservative health spokesman Andrew Lansley has formally called on the government to extend vaccination to all school children and college students. Mr Lansley says he's been pressing for this "behind the scenes" for weeks. Sir Liam says it's not a question of whether but when the programme is extended, but they are looking at the best way of doing it. He said an announcement would be made "within a couple of weeks".

Swine flu across the UK

My apologies to those who live outside England. This summary must appear rather England-centric. It's an inescapable fact that I can't get to the swine flu briefings outside London, but I do my best to reflect what's happening UK-wide. It would be great if the four health departments could get together and publish UK data as well as that representing their individual statistics.

To summarise, there have been slight falls in the number of suspected swine flu cases in Scotland and Wales, with a big decrease in Northern Ireland.

In Scotland 17,487 people are thought to have contracted swine flu over the last week, compared with 19,200 cases reported in the previous week.

In Northern Ireland, 215 laboratory-confirmed new cases have been reported in the last week, compared with 142 in the previous week - the department there does not seem to publish an estimated total of those infected, making comparisons difficult. Nonetheless, it does report GP consultations for flu and flu-like illness, which have decreased from the very high level of 280 per 100,000 to 222 in week 44 (21% decrease). Contrast that with the rate of 37.7 in England.

In Wales, 1,971 people contacted their GP in the last week with flu-like symptoms, compared with 2,626 the week before.

Justin McCracken, chief executive of the Health Protection Agency told journalists that in England, around 50% of patients who were being swabbed for suspected swine flu actually tested positive for the H1N1 virus. In Scotland and Wales, the rate is around 40%, while in Northern Ireland it is 80%.

Deaths

The overall number of deaths linked to swine flu now stands at 154 for the United Kingdom - 105 in England, 31 in Scotland, eight in Wales and 10 in Northern Ireland. The average age of those who've died is 44. Four out of five of those who've died have had some underlying health problem.

Useful resources:
Detailed UK weekly epidemiology update

Swine flu figures for Northern Ireland

Swine flu figures for Scotland

Swine flu figures for Wales

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