The sudden outbreak of a lethal virus that spreads quickly, killing millions, is a nightmare scenario that haunts many of us - especially those who have been watching BBC One's apocalyptic new drama Survivors.
Viruses have indeed wiped out 90 per cent of a human population. We've seen that in the Democratic Republic of Congo in 1976 with Ebola, an unspeakably nasty affliction caused by a haemorrhagic fever virus that has one of the highest case fatality rates of any human disease. It's one of a family of viruses that you definitely don't want to have, which also includes those responsible for Lassa fever and Marburg fever. But this event did take place in a very isolated area in a small population, with almost no access to medical help.
The lethality of these viruses limits their spread. People become so ill so quickly that they cannot travel far before dying. Ah yes, you say, (if you are the scriptwriter of Survivors), but what if someone boarded an aircraft immediately after infection but before symptoms appeared. Couldn't they spread it halfway across the world and kill 90 per cent of the population that way? No. Sorry to be a Survivors killjoy, but these viruses are pretty much stopped in their tracks by effective isolation and infection-control measures.
On the other hand, a candidate for a really good apocalypse virus is one that can be transmitted by droplet infection in the air, is infectious before a person has any symptoms and is not so lethal that people who have it can't spread it about by travelling. Something like flu, for instance. Pandemic flu is perfect.So would - could - pandemic flu wipe out 90 per cent of the population?
Categorically not, and for a number of reasons. One is logistics. You can't infect everyone at the same time, which means that we would have warning of potential infection and could prepare against it.
Avian flu poses a threat
The most likely (but by no means the only) pandemic flu candidate is H5N1, which causes avian flu in birds, such as chickens and ducks. At present, although human beings can be infected with avian flu and it has a high death rate (about 60 per cent), it is not spread from human being to human being. If it was, we would, thanks to the surveillance systems that the World Health Organisation has in place, know about it quickly, know where it was and could take counter measures. For instance, government might order mass vaccination with a pre-pandemic flu strain. This wouldn't be as effective as a vaccine specific to the particular strain, and would not necessarily prevent infection, but it is highly likely to prevent deaths.
But back to that scary old 60 per cent death rate with avian flu. Jonathan Van Tamm, Professor of Health Prevention at Nottingham University, did the numbers for me. “What this figure means is that 60 per cent of people who get ill with symptoms die, not 60 per cent of the population. It's a big difference.” To understand how many in a population might die from a new virus, you need to know the clinical attack rate, that is the proportion of the population that becomes ill with symptoms. Not everyone will be exposed to it and not all of those exposed are likely to develop symptoms and become sick.
If the clinical attack rate of a pandemic flu virus were, for example, 33 per cent (and not everyone would get it all at once of course, like in Survivors) and there was a case fatality rate of 60 per cent, 20 per cent of the population would die over the period of the pandemic, but this is unlikely.
As Professor Van Tamm says: “History tells us that, so far, we have never encountered a pandemic flu virus with a clinical fatality rate greater than 2.5 per cent (in 1918 it was 2.5 per cent; in 1957 and in 1968 it was less than 0.5 per cent). It's still an awful lot of people (280,000 in 1918) but nothing like the Survivors scenario.
A good plot line, and one that has been exploited in Survivors, is how panic and lack of preparation by government contributed to death rates. But here is the good news. As far as pandemic flu is concerned, which our Government regards as the No 1 threat facing the UK, Britain is among the best, if not the best, prepared countries in the world.
Lest you think this is hype, I took part in the G8 pandemic flu exercise in 2006, a simulation of a worldwide flu crisis in which all of the G8 nations took part. It was immediately apparent that this was the case. Most countries are woefully ill-prepared compared with us. If you want to check out the extensive and detailed plans for pandemic preparedness, they are on the Department of Health's website.
These plans have already been tested, in an exercise in January last year called Winter Willow. Lasting several days, it involved more than 5,000 people. It assumed an attack rate (those developing symptoms) of 30 per cent of the population. There were a number of lessons learnt, such as the need for clearer and more consistent advice on the use of antiviral drugs, face masks and the stocking of home supplies.
But there are other reasons why a flu pandemic is unlikely to mirror the Survivors outbreak. For instance, typically viruses do not retain their lethality. They are modified, with the passage through humans becoming more transmissible but less lethal with time.
Fit young men died within 24 hours
But perhaps the most potent reason is that we are not clones. Our immune systems are not all configured the same, our response to illness is highly variable, even when infected with the same virus. Typically, the old, sick and young would die, but even this isn't always the case. In the 1918 pandemic, fit young men died within 24 hours of infection, not from the virus but as a consequence of the “cytokine storm” unleashed by their healthy immune systems, which go into overdrive and attack the body while fighting the virus.
We are long overdue a flu pandemic. Expert opinion as to when it will happen varies between two and five years. It is certain that 90 per cent of us will not die. It is also certain that a flu pandemic would cause serious disruption to the economy, so, please, will everyone avoid hugging ducks in Asia - at least until we're done with this economic crisis.
PREPARING FOR A PANDEMIC
Face mask Wear only if you are in a frontline service caring for people who are sick.
Tamiflu In the case of avian flu, you could take Tamiflu to prevent infection, but you would have to take it for months, if not years, as successive flu waves swept the country.
Hygiene Use tissues and flush them away to avoid them infecting others. If you're out and about, wash your hands frequently as the virus is spread mainly by contact with surfaces touched by sufferers.
Stockpile food and water Only for the few days when you're too ill to go to the shops.
SECRETS OF A BORN SURVIVOR
Would you have the strength and resilience to cope in a post-apocalyptic world; one without supermarkets, running water and John Lewis? To find out what makes some people flounder and others flourish, the author Laurence Gonzales interviewed survivors of life-and-death situations.
His bestselling book Deep Survival:Who Lives, Who Dies and Why lists the characteristics that define a survivor. Although he gleaned this information from disaster situations, he says that it can apply to all kinds of crises.
Keep calm According to Gonzales, those who survive a disaster display two key traits. First, they don't panic. Secondly, they don't pretend that everything is going to be all right. It's not, and they realise that they have to take action to get themselves out of danger.
Get angry Everyone gets scared, but people who escape from burning buildings or sinking ships turn that fear into anger. This turns an immobilising emotion into a motivating one.
And organise According to his research, survivors quickly organise, make plans and institute discipline. Steve Callahan, a sailor who drifted alone on a 5ft raft for 76 days, said that he had the voice of a captain in his head, telling him to maintain water rations and keep panic at bay.
Never give up hope Survivors celebrate even the smallest successes, says Gonzales. And to stave off feelings of despair, they maintain a sense of humour and laugh at the stupidity of a scenario.
Stay decisive Survivors never dither. They make decisions but don't take stupid risks. Also, instead of looking at the big picture, which is likely to overwhelm and prompt despair, they take the situation minute by minute, hour by hour.
Believe in yourself Gonzales claims that those who survive report an unwavering belief that they will make it out of a situation. Lose hope and you're already defeated. But don't wait around for rescue. Survivors believe that everything they need to make it out of the situation is at their disposal.
Do whatever is necessary Those who survive, such as the lone hiker who had to cut off his arm to free himself from underneath a rock, keep their eyes on the goal and don't let anything else stand in the way.
Think of others The final secret of survival? Don't put yourself first. According to Gonzales, those who live through dangerous situations don't focus on surviving for personal reasons, but instead focus on surviving for the sake of friends and family back home.
And contrary to the scenes from the BBC One series, Survivors, where people kill each other for food and water, studies suggest that people are much more co-operative in disasters than we might think. Researchers at the University of Sussex looked at emergency situations by examining individual responses to various disasters, ranging from sinking ships to the London bombings of July 7, 2005.
They found that in each incident the common theme was the communal spirit between strangers. The researchers report that when a disaster happens, it causes a shared bond among those experiencing it as they become united against adversity.This causes them to act collectively, transcending their own personality differences.
“People move from being lonely individuals to a collective self; they feel part of something bigger and even take risks for complete strangers,” the researchers say.
According to this school of thought, it therefore becomes irrelevant if you are a narcissist or an extrovert, your behaviour is swayed by the adverse incident so that you become a group sharing a common goal, a group that thinks as a team.