Page last updated at 23:08 GMT, Saturday, 8 August 2009 00:08 UK

Pandemics - what history tells us

By Dr Mike Leahy
Virologist and presenter of Pandemic: A Horizon Guide


Preview clip of Pandemic: A Horizon Guide

Pandemic disease is only one aspect of nature that we still don't have the means to fully predict. Like the weather, it is virtually impossible to foresee with any certainty beyond a few days.

You might just as well study how far up a tree crows build their nests in a particular year, or check to see if it rains on St Swithin's Day.

Such are the limitations of science, whether meteorology or virology. The recent H1N1 or swine flu predictions have led to forecasts of 65,000 deaths in the UK - but the truth is, we simply don't know.

Yet in reporting the outbreak, the media broadly falls between two extremes - from alarming scare stories to experts who purport mass vaccination to be "madness, foolhardy and a gamble".

Whatever happens when the pandemic pans out, there will be a substantial third group - the "I told you so" faction. Pandemic disease remains a critical test of the extent of what we do and don't know.

Pandemics: A Horizon Guide shows how science and the media have grappled with widespread disease, reporting its failures and championing success.

Beating smallpox

Negative-stained image of swine flu virus
There have been some alarming swine flu predictions in the media

I have enormous faith in science - one of the high points in virology, if not the discipline's crowning achievement, was the eradication of smallpox from the world.

It was only one of many viruses that caused worldwide disease outbreaks but the dreadful suffering it caused made it an obvious target.

Understandably, once smallpox was eradicated some of the scientific community may have begun to believe that they could perhaps conquer all pandemic disease given time.

But in retrospect, smallpox was the ideal candidate for eradication.

The variola virus which caused the disease only infected humans, therefore giving it no natural hiding place such as mosquitoes, birds or mice.

And unlike many other viruses, it didn't mutate readily. This meant it couldn't adapt quickly enough to avoid our defences once we were immunised.

Unpredictable challenge

Unfortunately not all pandemics or pathogens are alike. Each is unique and poses its own challenges to science.

Malaria has been banished from Italy, the USA, the UK, and Poland (where it was endemic until the 50s), and is now predominantly a disease of the tropical poor.

American policeman wearing mask
The 1918 'Spanish flu' outbreak killed millions around the world

However, it still stubbornly resists any further attempts to eradicate it.

With scientific knowledge gained over the last 30 years, HIV has been shown to be a relatively difficult virus to contract and easily avoided with simple interventions.

For example, free condoms, needle banks, education, and behavioural changes.

Yet still it kills in the region of three million people each year (approx one person every 10 or 15 seconds).

And of course there is the most capricious of pathogens: influenza.

In 1918 an outbreak of H1N1 influenza virus killed somewhere between 22 and 100 million people.

However, when a broadly similar H1N1 strain emerged in the US in 1976 only one person died, although it did cause panic across the nation.

I would like to think that we can learn from history. So after making the Horizon programme, which looks at the history of pandemics as covered by TV over the last half century, there are some obvious lessons to be learned.

I think that the take-home message is that pandemics are to be feared and respected, but most importantly that they are incredibly difficult to predict.

Umbrellas in the rain
Like the weather, long range forecasts about virus development are imprecise

Maybe science will have a pretty good idea of what will happen to the swine flu pandemic in the next few days, but trying to predict beyond a few short weeks is much more challenging - much like the weather forecasts. All we can say in certainty is that H1N1 flu is, and will continue to be, unpredictable.

The influenza virologists, epidemiologists and computer modellers I know are diligent, skillful and inspirational people but they are ultimately up against nature.

I hope that in a few years I can take part in an updated pandemics guide and look at exactly what happened with this pandemic.

Then, with the benefit of hindsight, I might be able to say whether it was a storm in a teacup or whether we did too little too late. And find out who can say with total honesty "I told you so".

Pandemic: A Horizon Guide is on BBC Four on Sunday 9 August at 2200BST.

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