0:00:02 > 0:00:05Year on year, millions of people all over the world are affected
0:00:05 > 0:00:11by flu. Last year it killed nearly seven times more people than were
0:00:11 > 0:00:13killed in road traffic accidents.
0:00:13 > 0:00:17And every generation, a new strain emerges that can be catastrophic.
0:00:19 > 0:00:22Flu is one of the most difficult diseases for modern
0:00:22 > 0:00:27medicine to overcome, to predict or even to control. But why?
0:00:27 > 0:00:30Bang Goes The Theory investigates.
0:00:30 > 0:00:34I meet the volunteers infected with flu for medical research.
0:00:34 > 0:00:37This whole ward is in quarantine lockdown
0:00:37 > 0:00:41and the reason is on that trolley.
0:00:41 > 0:00:46Jem gets to grips with why flu is so successful year after year.
0:00:46 > 0:00:51This cascading explosion of viruses then burst back out of the cell membrane.
0:00:51 > 0:00:54This is what's known as an influenza infection.
0:00:54 > 0:00:57I'll meet the scientists trying to outmanoeuvre this
0:00:57 > 0:00:59unwittingly smart virus.
0:00:59 > 0:01:02The influenza virus is the great escape artist.
0:01:09 > 0:01:12This is a high-security quarantine zone.
0:01:12 > 0:01:16The people in here are receiving medical attention. But the
0:01:16 > 0:01:22doctors are not trying to cure them. They're trying to infect them with the flu virus.
0:01:22 > 0:01:28Because this is a clinical test to see how people deal with flu.
0:01:28 > 0:01:30Ten volunteers are infected,
0:01:30 > 0:01:34and their illness is monitored over three weeks to see how they fare.
0:01:34 > 0:01:37It's only through research like this that we can learn
0:01:37 > 0:01:39more about this virus.
0:01:40 > 0:01:42How dangerous is flu?
0:01:42 > 0:01:45In the UK we had about 12,500 deaths last year.
0:01:45 > 0:01:49If you expand that to worldwide, there was something like half a million.
0:01:49 > 0:01:51Then you have many more millions
0:01:51 > 0:01:54where there's severe illness, where they're incapacitated
0:01:54 > 0:01:56for a week or two or something,
0:01:56 > 0:01:59your young, elderly and immune-compromised.
0:01:59 > 0:02:03What's the difference between a cold and having flu?
0:02:03 > 0:02:07Generally it is the symptoms you present with.
0:02:07 > 0:02:11You can have your snotty, runny nose, a little bit of a headache, feeling unwell,
0:02:11 > 0:02:13but if you start presenting more systemic symptoms,
0:02:13 > 0:02:17you are feeling achy and have a temperature, that would probably be a good indicator.
0:02:17 > 0:02:20But ultimately we need to have the laboratory diagnosis
0:02:20 > 0:02:23to make that proper, formal diagnosis.
0:02:23 > 0:02:28So what is the flu virus, and why is it so particularly deadly?
0:02:31 > 0:02:35It's easy to think that flu is a modern disease.
0:02:35 > 0:02:39The press is full of how new flus are crossing from birds and pigs
0:02:39 > 0:02:42to humans in the markets of China.
0:02:42 > 0:02:45But actually its history as a human disease goes back
0:02:45 > 0:02:47a surprisingly long way,
0:02:47 > 0:02:49to about 10,000 years ago.
0:02:49 > 0:02:50Back then, big changes were
0:02:50 > 0:02:54happening in the way we Homo sapiens lived.
0:02:54 > 0:02:56We stopped being nomadic,
0:02:56 > 0:02:59and started setting up permanent homes in communities, and that's
0:02:59 > 0:03:03when many experts believe our flu problems began because we stopped
0:03:03 > 0:03:07hunting and gathering and started farming and domesticating animals.
0:03:10 > 0:03:14Until then, influenza was only an animal disease.
0:03:14 > 0:03:18It infected birds, horses, wild boar...
0:03:19 > 0:03:23And our contact with these animals was rare.
0:03:26 > 0:03:30But when we started to raise animals domestically,
0:03:30 > 0:03:33we brought them into direct, daily, physical contact
0:03:33 > 0:03:35with other animals and ourselves.
0:03:35 > 0:03:41And that's when a few viruses began to jump between species.
0:03:41 > 0:03:43In these primitive farms,
0:03:43 > 0:03:47many experts think that the virus first jumped from birds to pigs.
0:03:47 > 0:03:49And then it was just a matter of time
0:03:49 > 0:03:53until flu jumped again, to humans.
0:03:55 > 0:03:59Human influenza can be a huge killer.
0:03:59 > 0:04:02For instance, the 1918 outbreak of Spanish flu
0:04:02 > 0:04:05killed over 50 million people.
0:04:05 > 0:04:08But exactly how does the flu virus work?
0:04:14 > 0:04:18For the purposes of what we're going to try, this is a flu virus.
0:04:18 > 0:04:21Now, you may have heard flu viruses being given various names,
0:04:21 > 0:04:24like H5N1, H7N9.
0:04:24 > 0:04:27Well, they are important letters, those Hs and Ns,
0:04:27 > 0:04:29because they refer to the proteins
0:04:29 > 0:04:33that allow the virus to get in and out of cells within our body.
0:04:33 > 0:04:35So on our virus, these fittings here,
0:04:35 > 0:04:38these are like the Hs, the haemagglutinin.
0:04:38 > 0:04:42And this one here, that's the N, the neuraminidase.
0:04:42 > 0:04:46So there's the virus. Now, this is like the cell membrane.
0:04:46 > 0:04:48It actually coats the entrance to my workshop.
0:04:48 > 0:04:52This won't allow anything of this size through into the workshop,
0:04:52 > 0:04:54the interior of the cell.
0:04:54 > 0:04:56Once this virus drifts up towards the membrane,
0:04:56 > 0:05:01if it has the correct proteins, the correct haemagglutinin,
0:05:01 > 0:05:05it can...stick to the cell membrane.
0:05:05 > 0:05:09And once it's stuck on there, the cell will invite it inside.
0:05:11 > 0:05:15Once accepted, the cell membrane bulges in
0:05:15 > 0:05:18and the virus comes in with it.
0:05:18 > 0:05:21And then effectively seals back up again.
0:05:23 > 0:05:27There you go. Once inside, this coating
0:05:27 > 0:05:30starts dissolving away from the virus
0:05:30 > 0:05:32and it's able to float towards the nucleus,
0:05:32 > 0:05:35where it really starts doing the work.
0:05:35 > 0:05:40And this is exactly what's happening inside the bodies of our volunteers.
0:05:40 > 0:05:44The first of the flu viruses are passing into their cells.
0:05:44 > 0:05:46Although at this point, they don't even know they're sick yet.
0:05:46 > 0:05:49I'm feeling quite well at the minute.
0:05:49 > 0:05:52I'm ready for it to come on all of a sudden, but I feel all right.
0:05:52 > 0:05:56But inside their cells, the virus is starting to get to work.
0:05:56 > 0:05:59The exterior of the virus kind of gets unravelled
0:05:59 > 0:06:01as it travels through the fluid of the cell,
0:06:01 > 0:06:04revealing what's inside.
0:06:04 > 0:06:06Just eight genes.
0:06:06 > 0:06:13The genes are the instructions as to how to build a flu virus.
0:06:13 > 0:06:16Eight may seem like a lot, but it's not.
0:06:16 > 0:06:21In fact, we humans have over 23,000.
0:06:21 > 0:06:24And there's something else in the virus, too.
0:06:24 > 0:06:27There's a chemical called polymerase.
0:06:27 > 0:06:30We've represented this by a photocopier
0:06:30 > 0:06:33because essentially, it does the same job.
0:06:33 > 0:06:37It is the machinery required to copy these genes
0:06:37 > 0:06:40so that more viruses can be made.
0:06:40 > 0:06:42What it does now is pretty clever.
0:06:42 > 0:06:47Because it hijacks the materials within the nucleus of the cell
0:06:47 > 0:06:49and also its energy supply
0:06:49 > 0:06:52to allow it to do its dastardly work.
0:06:52 > 0:06:53Power going in.
0:06:55 > 0:06:58Genetic material being loaded.
0:06:59 > 0:07:01Gene instructions.
0:07:03 > 0:07:04And so the process begins.
0:07:13 > 0:07:16From when it enters the cell, within about five or six hours,
0:07:16 > 0:07:19the virus is able to make thousands of copies
0:07:19 > 0:07:21of its genetic instruction manual.
0:07:24 > 0:07:2812 hours later, more and more of the volunteers' cells are hijacked.
0:07:28 > 0:07:30Their immune system starts to react
0:07:30 > 0:07:33and the patients finally start to feel sick.
0:07:33 > 0:07:39Meanwhile, inside their cells, the virus is moving into a new phase.
0:07:40 > 0:07:43Then these new, freshly-minted sets of genetic material
0:07:43 > 0:07:47leave the nucleus and come out here, into the body of the cell,
0:07:47 > 0:07:51the cytoplasm, where they start using the stuff around them
0:07:51 > 0:07:54to assemble new viruses.
0:08:05 > 0:08:08And within 24 hours, the virus could have reproduced itself
0:08:08 > 0:08:10hundreds of thousands of times.
0:08:17 > 0:08:19Two days into the experiment,
0:08:19 > 0:08:23our volunteers are beginning to feel the full force of the infection.
0:08:23 > 0:08:26Tiredness, nausea and a sore throat.
0:08:26 > 0:08:29The virus is running amok.
0:08:29 > 0:08:33This cascading explosion of viruses being created here
0:08:33 > 0:08:35then burst back out of the cell membrane
0:08:35 > 0:08:39ready to cause more mayhem inside your body.
0:08:39 > 0:08:42This is what's known as an influenza infection.
0:08:45 > 0:08:46A day later, and the volunteers
0:08:46 > 0:08:49are showing the full range of classic flu symptoms,
0:08:49 > 0:08:53from chesty coughs to sinus headaches.
0:08:53 > 0:08:55My nose has been really, really painful,
0:08:55 > 0:08:57and, like, they wake you up at 6:00 in the morning,
0:08:57 > 0:09:01so when I was feeling really ill, I was just like, "Oh! Ow!"
0:09:01 > 0:09:03When the virus enters the body,
0:09:03 > 0:09:05there is an immediate immune response.
0:09:05 > 0:09:09The subject experiences fever, that is a rise in the temperature.
0:09:09 > 0:09:13That is one form of trying to kill the virus.
0:09:13 > 0:09:15The subject will experience a runny nose.
0:09:15 > 0:09:19And that runny nose is initially clear and watery.
0:09:19 > 0:09:22As the cells that are acting to kill the virus die,
0:09:22 > 0:09:25they are shed into the mucus.
0:09:25 > 0:09:27The consistency of the mucus then changes,
0:09:27 > 0:09:29to then being thick, greenish in colour.
0:09:29 > 0:09:32And that's how the symptoms will progress.
0:09:32 > 0:09:35But this patient's body is fighting back.
0:09:35 > 0:09:38And swelling in the neck is a sign that it's working.
0:09:38 > 0:09:41Because that's the location of the lymph nodes.
0:09:41 > 0:09:45Now, these lymph nodes will actually process the virus,
0:09:45 > 0:09:49the foreign body, soon realise that this is something that is harmful.
0:09:49 > 0:09:53The cells start working overtime and the gland starts enlarging.
0:09:53 > 0:09:56Because it now has to produce an immune response.
0:09:56 > 0:10:00And that's why the glands then start feeling painful,
0:10:00 > 0:10:01tender and enlarged.
0:10:03 > 0:10:05These glands are swollen
0:10:05 > 0:10:08because they are now pumping out cells to attack the flu.
0:10:08 > 0:10:11Cells called antibodies.
0:10:11 > 0:10:15Antibodies are special cells produced in the lymph glands
0:10:15 > 0:10:19that can recognise and destroy specific enemy viruses.
0:10:19 > 0:10:21So in the case of flu, for instance,
0:10:21 > 0:10:24they recognise the neuraminidase and the haemagglutinin
0:10:24 > 0:10:26on the surface of the virus.
0:10:26 > 0:10:30Once recognised, the lymph glands go into overdrive,
0:10:30 > 0:10:32producing billions of antibodies
0:10:32 > 0:10:35which then destroys the virus.
0:10:35 > 0:10:38But the flu virus can fight back.
0:10:39 > 0:10:43And they can do this because of a weakness in the copying process
0:10:43 > 0:10:46at the heart of the invaded cell.
0:10:46 > 0:10:49Now, if this copying process was absolutely perfect
0:10:49 > 0:10:52and made identical copies every time,
0:10:52 > 0:10:56the human's defence systems would soon recognise that virus
0:10:56 > 0:10:57and learn to kill it.
0:11:00 > 0:11:04But crucially, the inadvertent genius of the virus
0:11:04 > 0:11:07is that the copying process is not quite perfect.
0:11:07 > 0:11:12And every now and again, it makes a set of instructions
0:11:12 > 0:11:14that aren't quite the same as the original.
0:11:14 > 0:11:17And those instructions then end up building a virus
0:11:17 > 0:11:19that isn't quite the same as the original.
0:11:19 > 0:11:23And that can result in a mutant virus.
0:11:23 > 0:11:26And here you see there's been a subtle change.
0:11:26 > 0:11:28A little bit of difference in the neuraminidase
0:11:28 > 0:11:31and a little bit of difference in the haemagglutinin.
0:11:31 > 0:11:35And these tiny differences are, in fact, what makes all the difference.
0:11:40 > 0:11:42When the new mutant virus emerges
0:11:42 > 0:11:45with its subtly-altered protein groups,
0:11:45 > 0:11:47the body's police don't recognise it.
0:11:50 > 0:11:53This process of evolving and changing to avoid detection
0:11:53 > 0:11:57by the immune system is known as antigenic drift.
0:11:57 > 0:12:02And the result is this virus can carry on and attack with impunity.
0:12:02 > 0:12:07But we have one powerful weapon against this kind of flu.
0:12:07 > 0:12:09We can vaccinate.
0:12:12 > 0:12:16At any point in time, there are hundreds of different types of flu strain
0:12:16 > 0:12:18circulating in the population.
0:12:18 > 0:12:23And with modern travel, these are moving across the globe like never before.
0:12:23 > 0:12:27Here at the National Institute for Medical Research in London,
0:12:27 > 0:12:30teams of scientists work day and night
0:12:30 > 0:12:33to find vaccines for the most dangerous strains
0:12:33 > 0:12:34before they can reach our shores.
0:12:38 > 0:12:43For us to decide what virus we want to use as a vaccine,
0:12:43 > 0:12:45we have a global surveillance system
0:12:45 > 0:12:48which is organised under the WHO, the World Health Organisation.
0:12:50 > 0:12:53The first step in making vaccines
0:12:53 > 0:12:55is collecting thousands of nasal swabs
0:12:55 > 0:12:59from suspected influenza cases from all over the world.
0:12:59 > 0:13:02We get specimens from virtually every country in Europe.
0:13:02 > 0:13:07We go as far away as Hong Kong, South Africa, Argentina, anywhere.
0:13:10 > 0:13:13Hundreds of these swabs arrive at the lab every day
0:13:13 > 0:13:16and each has to be painstakingly analysed.
0:13:19 > 0:13:23They are injected and incubated in egg yolks, where they multiply.
0:13:28 > 0:13:31And after a few days, the viruses can be removed and tested.
0:13:35 > 0:13:37What are we looking at here, then?
0:13:37 > 0:13:42Where you see dots, that means we have no virus.
0:13:42 > 0:13:45But where you see the red blood cells held in suspension,
0:13:45 > 0:13:47that means we have virus growing.
0:13:47 > 0:13:51- So we've got infectious virus here, here, here.- Yes.
0:13:51 > 0:13:56Thousands of flu strains are isolated like this,
0:13:56 > 0:13:59but then the team have to work out the five or six strains
0:13:59 > 0:14:01which are most likely to spread globally.
0:14:03 > 0:14:06To do this, they study each virus' history.
0:14:06 > 0:14:08This is the bible, is it?
0:14:08 > 0:14:12This file contains the information we went through last September
0:14:12 > 0:14:14to make vaccine decisions.
0:14:15 > 0:14:17The file provides details about the flu viruses
0:14:17 > 0:14:21collected from around the world and how they are evolving.
0:14:22 > 0:14:24This shows an evolutionary tree.
0:14:24 > 0:14:28And we're starting here with what used to be a virus, Perth 16,
0:14:28 > 0:14:30which was a 2009 virus,
0:14:30 > 0:14:34and up here, we're getting into 2013 viruses.
0:14:34 > 0:14:37- So you can see how the virus has evolved.- Oh, yeah, yeah, yeah.
0:14:37 > 0:14:41And each of these little branches is an independent virus.
0:14:41 > 0:14:45Within all this data lie the clues that can tell us
0:14:45 > 0:14:48which new strains are likely to spread and cause havoc.
0:14:49 > 0:14:54So you have to ensure you have the very latest viral strain
0:14:54 > 0:14:59and then focus on that one to make a vaccine for the following year.
0:14:59 > 0:15:02- Yes, but we draw on the world picture.- Yeah.
0:15:02 > 0:15:05Because if it was just happening in one small community,
0:15:05 > 0:15:08one isolated country somewhere,
0:15:08 > 0:15:12we would keep an eye on it, but wouldn't necessarily change the vaccine.
0:15:12 > 0:15:15But if it was popping up in the US, in Europe, in Australia...
0:15:15 > 0:15:16- Then it gets interesting.- ..bang!
0:15:16 > 0:15:19- That's the vaccine for next year. - Yeah.
0:15:19 > 0:15:22But flu seems to always be one step ahead.
0:15:22 > 0:15:25It takes a minimum of six months to produce,
0:15:25 > 0:15:28test and distribute the vaccine.
0:15:28 > 0:15:32And in that time, this new flu strain could mutate yet again.
0:15:33 > 0:15:36The influenza virus is the great escape artist.
0:15:36 > 0:15:39It is able to change its surface genes
0:15:39 > 0:15:41to escape host immune responses
0:15:41 > 0:15:43and so we are perpetually chasing it
0:15:43 > 0:15:46rather than catching up and getting ahead of it.
0:15:46 > 0:15:49- You won't be out of a job any time soon, will you?- Certainly not.
0:15:50 > 0:15:54Vaccines are a powerful weapon against flu,
0:15:54 > 0:15:56but they are never going to beat it completely.
0:15:56 > 0:16:00And crucially, many people just don't like getting vaccinated.
0:16:00 > 0:16:04So oftentimes, the people who need them the most, like pregnant women,
0:16:04 > 0:16:06aren't protected.
0:16:06 > 0:16:09But a new vaccination policy could change all that.
0:16:14 > 0:16:17Currently, we vaccinate the people most at risk
0:16:17 > 0:16:19so they're less likely to get ill.
0:16:20 > 0:16:23But perhaps this is the wrong way round.
0:16:23 > 0:16:25Perhaps we should vaccinate the people
0:16:25 > 0:16:28most likely to spread the virus in the first place.
0:16:29 > 0:16:32Then the vulnerable wouldn't ever be exposed to it.
0:16:34 > 0:16:36And new research is beginning to pinpoint
0:16:36 > 0:16:39who is spreading flu fastest.
0:16:43 > 0:16:47Five years ago, Dr Alma Adler started to investigate.
0:16:47 > 0:16:51Since then, she has been recruiting children, teenagers and adults
0:16:51 > 0:16:54to fill in an online flu questionnaire
0:16:54 > 0:16:57to help pinpoint where the disease is actually coming from.
0:16:57 > 0:17:00If everyone could just click where it says, "Log in."
0:17:00 > 0:17:04Every year, the Flusurvey has been attracting thousands of users,
0:17:04 > 0:17:07all giving the details of their lives
0:17:07 > 0:17:09and when and how they are having flu.
0:17:11 > 0:17:15What we're able to show is the rates of flu in the youngest age groups,
0:17:15 > 0:17:17so in 0-18 year olds,
0:17:17 > 0:17:20tended to peak before the older age group.
0:17:20 > 0:17:23So you could see that you start to get increasing rates of flu
0:17:23 > 0:17:26in the younger age group and then a week or so later,
0:17:26 > 0:17:29the older age groups would start to go up.
0:17:31 > 0:17:34The Flusurvey revealed where flu was actually coming from.
0:17:34 > 0:17:37It was being spread by children.
0:17:40 > 0:17:45When you had flu, who remembers maybe passing it to someone else?
0:17:45 > 0:17:48Your mums or your dads said, "Oh, you've given me flu!"
0:17:48 > 0:17:51OK, so, um... Right, there. Yes?
0:17:51 > 0:17:53It was a nightmare for my family
0:17:53 > 0:17:56because I passed it to my brother and sister
0:17:56 > 0:17:58and then they somehow passed it to my mum and dad.
0:17:58 > 0:18:00Who else have you passed it onto?
0:18:00 > 0:18:04I also gave it to my other half of my family,
0:18:04 > 0:18:07so the whole of my family was sick.
0:18:07 > 0:18:10OK, so the whole family was ill.
0:18:12 > 0:18:15School kids are constantly touching each other,
0:18:15 > 0:18:17so if one has an infection,
0:18:17 > 0:18:21it's likely to move between them. And fast.
0:18:21 > 0:18:23But then the kids were passing the flu
0:18:23 > 0:18:25on to their parents and grandparents
0:18:25 > 0:18:28and into the high-risk groups.
0:18:30 > 0:18:33And this suggested to Dr Adler a new way to control flu
0:18:33 > 0:18:36was to stop it spreading at source.
0:18:36 > 0:18:38To vaccinate kids.
0:18:38 > 0:18:41If you vaccinate school-age children, they're going to get protected,
0:18:41 > 0:18:43but there's more to it than that.
0:18:43 > 0:18:46The theory behind it is that by vaccinating school-aged children,
0:18:46 > 0:18:49you're getting the direct effects on those children
0:18:49 > 0:18:52as well as the indirect effects to people they come into contact with,
0:18:52 > 0:18:56so their parents and their carers, on an everyday basis.
0:18:56 > 0:18:58They've come to the conclusion that
0:18:58 > 0:19:01the best way of reducing the number of flu cases
0:19:01 > 0:19:05is to vaccinate children between the ages of five and 16.
0:19:05 > 0:19:07So this year, vaccination in children
0:19:07 > 0:19:11is piloting in some schools in England and Scotland.
0:19:11 > 0:19:16And unlike the adult vaccine, this is administered nasally.
0:19:16 > 0:19:19It's hoped this revolutionary child vaccination
0:19:19 > 0:19:23might make a serious impact on the spread of seasonal flu.
0:19:23 > 0:19:26How did it feel?
0:19:26 > 0:19:27I didn't really feel anything.
0:19:27 > 0:19:30Is it something you'd be willing to have again next year?
0:19:30 > 0:19:32I'll be looking forward to it.
0:19:36 > 0:19:38But there is a different type of outbreak
0:19:38 > 0:19:41that can cause far more serious problems.
0:19:41 > 0:19:44And it seems to come around about once every generation.
0:19:46 > 0:19:47It's called pandemic flu,
0:19:47 > 0:19:50and we recently saw just how dangerous that can be.
0:19:52 > 0:19:53The number of deaths in Britain
0:19:53 > 0:19:56linked to swine flu has jumped to 29.
0:19:56 > 0:19:59'It's reckoned there were 55,000
0:19:59 > 0:20:02'new cases of swine flu last week across the UK.'
0:20:02 > 0:20:07Between one and 3.5 people in the thousand who catch it might die.
0:20:07 > 0:20:12That could mean anything from around 3,000 to 65,000 deaths
0:20:12 > 0:20:13from swine flu.
0:20:14 > 0:20:19For Charles Gardiner, catching swine flu was a life-changing experience.
0:20:19 > 0:20:23In 2009, he caught what he thought was a common cold,
0:20:23 > 0:20:26but it rapidly became much worse.
0:20:28 > 0:20:32I don't know if it's a mother's feeling, gut feeling,
0:20:32 > 0:20:35that things really weren't right with him.
0:20:35 > 0:20:37Terrible coughing and sweats
0:20:37 > 0:20:40and really gagging to get his breath. And I was really frightened.
0:20:40 > 0:20:43That was like the start of the nightmare, really,
0:20:43 > 0:20:46and we seemed to spiral from that moment
0:20:46 > 0:20:49and we were rushed to intensive care.
0:20:49 > 0:20:53All I remember is being at home and then just being so hot.
0:20:53 > 0:20:56Like, just... I remember being on Facebook
0:20:56 > 0:21:00and my status was, "I'm on fire, like, right now."
0:21:00 > 0:21:02That was literally the last thing I remember.
0:21:02 > 0:21:05His health quickly deteriorated
0:21:05 > 0:21:09and over the next weeks, the flu showed no mercy.
0:21:09 > 0:21:13He contracted double pneumonia, suffered heart stoppages
0:21:13 > 0:21:15and multiple organ failure.
0:21:15 > 0:21:18What could we do? I just obviously never left the hospital.
0:21:18 > 0:21:21I was in the little room next to him.
0:21:21 > 0:21:24And to see him like that, for such a big, healthy boy,
0:21:24 > 0:21:27you know, just sort of...
0:21:27 > 0:21:30I just couldn't believe it, how it all went.
0:21:31 > 0:21:33But Charles fought back.
0:21:33 > 0:21:36As a former England Under-21 international rugby player,
0:21:36 > 0:21:39he was made of stern stuff.
0:21:39 > 0:21:42You realise these were just stages of the swine flu
0:21:42 > 0:21:44and you just hope you're going to come out the other end of it,
0:21:44 > 0:21:47but you don't see it like that at the time, you just think,
0:21:47 > 0:21:50"Oh, you know, this is... We're not going to get through it, are we?"
0:21:50 > 0:21:52But we've got to, you know.
0:21:52 > 0:21:56Really fighting for every minute, every step of the way for him.
0:21:57 > 0:22:01Four years on and Charles has almost made a complete recovery.
0:22:02 > 0:22:05Now you look back on it and you realise how lucky you are.
0:22:05 > 0:22:10And now I don't have any long-term effects on my body or anything.
0:22:10 > 0:22:13I am just so lucky to be like that now. Yeah.
0:22:13 > 0:22:17When I heard his voice again, I thought, "Is that going to be different?"
0:22:17 > 0:22:19They said, "He'll probably be very different,"
0:22:19 > 0:22:22but he's not. He's just still Charles.
0:22:27 > 0:22:28Thankfully for most people,
0:22:28 > 0:22:32this pandemic wasn't as devastating as first predicted.
0:22:32 > 0:22:36But pandemics are more serious than seasonal flu because
0:22:36 > 0:22:39they are brand-new flu strains that emerge from animals.
0:22:39 > 0:22:42Flu viruses can cause pandemics
0:22:42 > 0:22:47when occasionally their surface antigens change almost completely.
0:22:47 > 0:22:50Now, this results in a fundamentally-new virus strain,
0:22:50 > 0:22:53which virtually no-one has been exposed to before
0:22:53 > 0:22:54or raised antibodies against.
0:22:54 > 0:22:56But how does this happen?
0:22:59 > 0:23:02OK, so here's our flu virus again
0:23:02 > 0:23:07with its eight genes inside it.
0:23:07 > 0:23:10And we know how easily viruses from animals like pigs
0:23:10 > 0:23:12can transmit over to humans,
0:23:12 > 0:23:16but the thing is, animals can also be a very good source
0:23:16 > 0:23:18of entirely-new strains of flu
0:23:18 > 0:23:21that can potentially be much more dangerous to us
0:23:21 > 0:23:24than the annual seasonal flu we're affected by.
0:23:24 > 0:23:27And that's because animals can be infected
0:23:27 > 0:23:31by two or more viruses at the same time.
0:23:31 > 0:23:34Now, imagine this bale of hay is our cell
0:23:34 > 0:23:37and you have two viruses infecting it.
0:23:37 > 0:23:42Each different strain will have its own unique set of genes.
0:23:42 > 0:23:45Now, during replication, some genes from one virus
0:23:45 > 0:23:49can get mixed up with the genes from the other.
0:23:49 > 0:23:52And this can produce a brand-new virus,
0:23:52 > 0:23:55each containing some genes
0:23:55 > 0:23:58from each of the original viruses.
0:23:58 > 0:24:02And because it's a mix of genes from two separate strains,
0:24:02 > 0:24:04the result is a novel virus.
0:24:04 > 0:24:09And this is called antigenic shift. And it's what can lead to pandemics.
0:24:09 > 0:24:11Because no-one has been exposed to this new strain,
0:24:11 > 0:24:14or raised antibodies against it.
0:24:15 > 0:24:18And this lack of immunity means occasionally,
0:24:18 > 0:24:21these pandemic flu have the potential to be catastrophic.
0:24:28 > 0:24:32In the spring of 1918, World War I was beginning to draw to an end.
0:24:35 > 0:24:37Millions had already died.
0:24:37 > 0:24:41And then a flu pandemic broke out.
0:24:41 > 0:24:43It was called Spanish flu.
0:24:45 > 0:24:49Some experts believe it started in a village in northern France,
0:24:49 > 0:24:52others believe it started in the Far East,
0:24:52 > 0:24:55but either way, its effects were overwhelming.
0:24:55 > 0:24:59Spanish flu was a particularly infectious strain.
0:24:59 > 0:25:01So aggressive, in fact, that many believe
0:25:01 > 0:25:05it caused what's known as a cytokine storm,
0:25:05 > 0:25:08a massive overreaction of the immune system.
0:25:08 > 0:25:10And it wasn't just the very young,
0:25:10 > 0:25:12the weak or the elderly who were affected.
0:25:12 > 0:25:15Because the immune response goes into overdrive,
0:25:15 > 0:25:18it was actually healthy young adults with a strong immune system
0:25:18 > 0:25:20who succumbed the most.
0:25:20 > 0:25:25Within 18 months, half the world's population had been infected
0:25:25 > 0:25:29and at least 40 million people, some say up to 100 million, had died.
0:25:31 > 0:25:35Since then, we've witnessed three other flu pandemics.
0:25:37 > 0:25:39The less-severe outbreaks of Asian flu in '57
0:25:39 > 0:25:43and Hong Kong flu in '68.
0:25:43 > 0:25:46And, of course, the most recent, swine flu in 2009,
0:25:46 > 0:25:48when another new strain leapt from pigs
0:25:48 > 0:25:51to a five-year-old child in Mexico.
0:25:51 > 0:25:55Within six weeks, this had also become a global pandemic.
0:25:56 > 0:26:00It's estimated that up to 300,000 people may have died from swine flu,
0:26:00 > 0:26:04but most suffered the symptoms and then fully recovered,
0:26:04 > 0:26:07so this time, we were relatively lucky.
0:26:13 > 0:26:15Outbreaks like these are completely unpredictable
0:26:15 > 0:26:18and they spread in a matter of weeks,
0:26:18 > 0:26:21so it's not possible to develop a vaccine.
0:26:21 > 0:26:25Our current course of action is a group of drugs known as antivirals,
0:26:25 > 0:26:28like Tamiflu or amantadine.
0:26:28 > 0:26:32And these work by attacking the virus as it enters the cell.
0:26:32 > 0:26:35But the virus evolves. It develops immunity
0:26:35 > 0:26:39and these drugs then become less effective.
0:26:41 > 0:26:43Currently, the best way to beat a flu epidemic
0:26:43 > 0:26:46is something we all should be doing anyway.
0:26:46 > 0:26:49Protect ourselves and others from getting the virus
0:26:49 > 0:26:51by washing our hands scrupulously.
0:26:51 > 0:26:53Now, you've got to do this properly,
0:26:53 > 0:26:57so you start by really giving your hands a good rinse,
0:26:57 > 0:26:59then you need to soap properly.
0:26:59 > 0:27:02And by soaping properly, that means working between your fingers,
0:27:02 > 0:27:04scrubbing away at your nails.
0:27:04 > 0:27:07And the whole process should take between one and two minutes.
0:27:07 > 0:27:09Do that frequently.
0:27:09 > 0:27:13And that is it. It really is as simple as that.
0:27:20 > 0:27:22And, if you are caught out without a tissue,
0:27:22 > 0:27:24sneeze into the crook of your arm.
0:27:24 > 0:27:27It might sound disgusting, but it's so much better than hosing the room
0:27:27 > 0:27:30or catching the sneeze in your hand and spreading it everywhere.
0:27:33 > 0:27:37Despite years of flu research, there's still much we don't know.
0:27:37 > 0:27:40This year was a mild flu year,
0:27:40 > 0:27:41but whether that was due to the warm winter,
0:27:41 > 0:27:45the rain or a genetic quirk remains a mystery.
0:27:45 > 0:27:48Either way, it'll be interesting to see
0:27:48 > 0:27:52whether that new vaccination strategy made a difference.
0:27:52 > 0:27:55But we still live under the threat of something more deadly.
0:27:55 > 0:27:57A flu pandemic.
0:27:57 > 0:28:00And only constant surveillance and scrupulous hygiene
0:28:00 > 0:28:04can help us from that unlikely, but terrifying possibility.
0:28:11 > 0:28:14Next week on Bang, the science behind flooded Britain
0:28:14 > 0:28:17and what we can all do to make sure it never happens again.
0:28:21 > 0:28:24If you want to find out more about careers in immunology,
0:28:24 > 0:28:27check out the website at www.bbc.co.uk/bang.
0:28:27 > 0:28:31And if you want to take part in the Open University's own flu survey,
0:28:31 > 0:28:35follow the links to their interactive pages.