Are we due another lethal global flu pandemic?

[Guest guest]

Are we due another lethal global flu pandemic?

Mar 10 2008 by Madeleine Brindley, Western Mail

The highly pathogenic H5N1 strain of bird flu is regarded by some to

be the most likely cause of the next human flu pandemic. But is there

any truth in the fears or, like the threat of Sars that never was, is

this just hype? Health Editor Madeleine Brindley reports

ON the basis that the last flu pandemic was almost 40 years ago and

that they occur every three to four decades, it would appear that we

are overdue such a global event.

The emergence of the highly pathogenic H5N1 strain of bird flu, and

the deaths of more than 300 people from this virus, mainly in

South-East Asia, has only added to that sense of foreboding.

But is a pandemic – which has the potential to kill tens of millions

of people worldwide – really imminent? And will H5N1 be the cause?

Flu pandemics are different to the seasonal flu viruses, which

circulate in the community every winter. They occur when a new

influenza virus, which people have no immunity to, emerges and starts

spreading as easily as normal flu.

Sir Liam son, the English chief medical officer, said, at the

launch of his 2005 annual report, " We do not know what the virus is

that will cause pandemic flu.

" What we do know is that Mother Nature has the recipe book and its

just a matter of time before she starts cooking. "

H5N1 is a severe – highly pathogenic – form of bird flu, which has

been affecting poultry flocks and other birds across the world since

2003. It was discovered in January in wild swans in Dorset.

But the virus is not simply confined to birds. Since it first emerged

there have been 366 cases of infection in people who have had close

and direct contact with infected birds – at the end of February, 232

of these people have died.

And yet despite this alarming death rate, there is – as yet – no

evidence that H5N1 has acquired the ability to pass easily from person

to person, making it a relatively minor threat to human health.

However, experts remain concerned that the virus might develop this

ability, or that it might mix with existing human flu viruses to

create a new virus.

It is this ability of avian influenza to change and to mix, that has

given rise to the fear of a new human flu pandemic.

Every winter heralds the start of a new flu season in Wales and the

rest of the northern hemisphere.

Some years are worse than others. This winter has seen relatively low

levels of flu activity in Wales, albeit the UK level was high enough

to give GPs the authority to prescribe antiviral drugs such as Tamiflu

and Relenza.

A pandemic, on the other hand, occurs on a much greater scale,

spreading around the world and affecting many hundreds of thousands of

people across many countries.

Three flu pandemics have occurred in the last century – 1918 to 1919

(Spanish flu); 1957 to 1958 (Asian flu) and 1968 to 1969 (Hong Kong flu).

Each of these pandemics affected large numbers of the population,

causing millions of deaths and huge economic and social disruption.

Sir Liam son said, " Wherever in the world a flu pandemic starts,

perhaps with its epicentre in the Far East, we must assume we will be

unable to prevent it reaching the UK.

" When it does, its impact will be severe in the number of illnesses

and the disruption to everyday life. "

And Professor Neil Ferguson, director of the MRC Centre for Outbreak

Analysis and Modelling said, " In the past we have had flu pandemics

every 20 to 30 years – 1918 is always remembered as the big one but

the records show that there was one in 1889 and all the way back to

the 16th and 17th centuries.

" The thing to worry about bird flu is it jumping into humans and then

spreading – but that hasn't happened yet.

" H5N1 is not the most likely strain to cause a pandemic. It has got

all the headlines but it is not the most common strain in birds.

" But the consequences of an H5N1 pandemic could be much worse because

it is so lethal – if that strain did cause a pandemic, we could be

something as bad as 1918 or even worse.

" In the 1918 pandemic 50 million people died worldwide from a

population on the planet of just over one billion people.

" The overall mortality was very high at about 5%. It was much lower in

the UK and US, but higher again in countries like India. "

There are three main groups of flu viruses – influenza A, B and C.

Influenza B and C viruses only infect people, but influenza A viruses

have the ability to cross the species barrier and infect people,

birds, and animals such as pigs and horses. Among people, influenza A

is the source of most " ordinary " flu epidemics and has caused all the

previous flu pandemics.

Experts fear that the H5N1 strain of avian influenza A could trigger

the next pandemic, for a number of reasons, not least because it has

already demonstrated an ability to infect people and cause severe

disease – one of the key characteristics of a pandemic strain.

The virus also has the ability to mutate and acquire genes from

viruses infecting other species.

Experts are worried that the virus could either adapt, giving it

greater affinity for humans, or exchange genes with a human flu virus,

thereby producing a completely new virus strain capable of spreading

easily between people, and causing a pandemic.

Alternatively the pandemic could arise from a strain of influenza A

unrelated to H5N1.

A spokesman for the National Public Health Service for Wales, said,

" Any strain of the flu virus could mutate to cause a pandemic in

people. But of the strains that are around at the moment, it is the

avian flu virus H5N1 that seems most likely to do this. "

If a pandemic strain were to occur then few people, if any, would have

a natural immunity to it. Exposure to ordinary seasonal flu would not

provide any immunity.

Prof Ferguson, who is also a professor of mathematical biology at

Imperial College, London, said, " The risk of a pandemic has been

hyped, in the sense that many people believe that it is imminent – I

don't think it is.

" A pandemic is a one-in-30- year event, but just because we haven't

had one for 30 years, doesn't mean that we are due one.

" It could happen next year, but my own evaluation is that this is a

low-probability event, with a one in 200 or a one in 100 chance of H5N1.

" But it could be so lethal, given that the virus kills so many birds,

that the possibility of having a catastrophic pandemic means that we

should be preparing for it and putting resources into it. We should be

making those preparations reasonably urgently.

" I have been a little concerned about some points of the preparedness

plan – last year it was starting to slip down the agenda.

" I'm very pleased that the Government has this year announced a

doubling of antiviral drug stocks.

" Pandemic flu is one of the top five priorities for the NHS, although

it is not going to be in the top five of spending, but the Government

is still taking the plans seriously. "

The World Health Organisation has developed a global alert system,

based on six pre-defined phases, as a way of signalling the

seriousness of the risk of an influenza pandemic.

The world is currently at phase three, meaning that a new influenza

virus subtype is causing disease in humans, but is not yet spreading

efficiently and sustainably among humans.

Prof Ferguson added, " I wouldn't recommend that people start

stockpiling their own drugs or anything like that in the event of

pandemic flu.

" It could happen next year but it is more likely to be in five or 10

years' time. It is a case of keeping yourself informed and being aware

of what a pandemic would be like.

" Life won't stop altogether. "

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