Warning: Dr Jonathan Quick is Chair of the Global Health Council

The big one is coming: a global virus pandemic that could kill 33 million victims in its first 200 days.

Within the ensuing two years, more than 300 million people could perish worldwide.

At the extreme, with disrupted supply of food and medicines and without enough survivors to run computer or energy systems, the global economy would collapse. Starvation and looting could lay waste to parts of the world.

It’s a disaster movie nightmare. Yet it is waiting to come true, thanks to influenza — the most diabolical, hardest-to-control and fastest-spreading potential viral killer known to humankind.

As a medical doctor and a health chief who has led global programmes at the World Health Organisation (WHO), I believe that the world is at risk of a viral pandemic that will be at least as deadly as anything we have ever known before.

The most likely culprit will be a new and unprecedentedly deadly mutation of the influenza virus. The conditions are right. It could happen tomorrow.

The good news is that there is much we can do to prevent this. The bad news is that much of it is not being done.

We are just as vulnerable now as we were 100 years ago, when the 1918 Spanish flu pandemic infected a third of the world’s population and wiped out up to 100 million people. It remains the deadliest flu outbreak in history.

A century on, the history and biology of the influenza virus tells us that we should expect another major global pandemic soon. Experts say it is already overdue.

Human influenza usually starts with wild aquatic birds, because avian flu is very common in waterfowl.

Once in a while, a wild bird virus gets friendly with a different strain inside another bird, or even a pig. The different strains can then swap genes, effectively swapping skills such as being highly contagious or deadly.

Wipeout: He fears a major influenza outbreak could kill 300 million people in two years

Somewhere out there, a flu virus is boiling up in the bloodstream of a bird, bat, monkey or pig, preparing to jump to a human being.

When that combination from birds and beasts finds its way into a person, the resulting new human strain can kill us more easily because it is unknown to us and our bodies have zero immunity to it. This is most likely how the Spanish flu took hold.

We have inadvertently developed a powerful way of helping influenza to kill us, 100 years on. This is our addiction to cheap chicken and pork — and the factory farm industry that supplies it.

Factory farms present one of the greatest potentials for catastrophic disease because they pack animals together by the million in conditions that can be fetid incubators of disease.

These giant industrial farms were the birthplace of H1N1 swine flu that emerged in 2009 and killed up to an estimated 575,400 people worldwide.

Scientists traced the virus’s genes to a massive North Carolina pig farm in 1998. Originally, the virus contained three human flu genes. Within a few months at the farm, it had acquired segments of two bird flu genes as well.

Pigs eat almost everything, so their guts are the perfect mixing bowls for flu strains. When pigs eat droppings of sick wild birds or the chickens living near them, the flu viruses in their digestive systems can swap their genetic material to create new strains.

Food for thought: Factory farms could very likely be the birthplace of the next killer pandemic

Pig guts can add multiple germs from the humans that the pigs come into contact with, too.

When new flu strains acquire their genes, it makes it easier for them to infect people.

Factory farms could very likely be the birthplace of the next killer pandemic. The renegade influenza viruses they spawn could one day annihilate the people they feed.

Reducing the risk posed by farm animals requires us all to fight factory farming. We can vote with our mouths. If we eat meat or dairy products, we can eat them less often, choose meat labelled organic (which, in the UK, is generally reared without routine antibiotics) and buy from places that don’t rely on factory farm sources (goodbye, High Street fast-food chains).

The most frightening type of infectious flu we know of today — the H5N1 strain of the virus (known popularly as ‘bird flu’) — also came from an animal. It probably jumped to a human through contact with a diseased bird slaughtered on a poultry farm or in one of Hong Kong’s markets.

H5N1 killed its first human victim in 1997 in Hong Kong. From 2003 to the start of 2016, there have been 846 confirmed human cases of H5N1 virus infection in 16 countries.

That may not sound like many people. At the moment, H5N1 is not very contagious. But this strain has killed more than half the people it has infected. By comparison, the Spanish flu epidemic of 1918 had a mortality rate of between just 2 and 3 per cent.

This makes H5N1 one of the deadliest viruses scientists have ever come across. It’s still very much out there: it continues to stir in the blood soup of chickens and ducks. Meanwhile, swine flu still mutates in the blood of pigs and remains a threat to humans.

'The most important thing that humankind can do, however, is to develop a properly effective universal vaccine against flu viruses', he urges

If a new and highly contagious strain of H5N1 were to evolve and hitchhike with an unwitting passenger on to a cruise ship or an aeroplane, the pandemic situation would quickly assume disaster movie proportions.

Therefore, to keep ourselves, our children and their children alive, nothing is more important than fighting these viruses.

We must pay proper heed to Public Health England’s ‘Catch It, Bin It, Kill It’ campaign. This encourages people to adopt good respiratory and hand hygiene, such as using a tissue and washing hands thoroughly. It really is an effective line of defence.

If you do get ill, you must protect others by staying home from work. We know from experience in American cities that encouraging people with flu to stay at home can cut transmission rates by half.

The most important thing that humankind can do, however, is to develop a properly effective universal vaccine against flu viruses.

As a doctor, I know that nothing can protect people against illness as effectively as a vaccine. It is the single most cost-effective public health tool we have.

As a doctor, I know that nothing can protect people against illness as effectively as a vaccine. It is the single most cost-effective public health tool we have. Dr Jonathan Quick

Such an innovation could limit, and possibly even prevent, a calamitous global influenza pandemic. But the search for a universal flu vaccine is late in coming. It was only in 2011 that The Lancet published research that demonstrated the inadequacy of our flu vaccines.

Today’s seasonal flu vaccination does not protect you from all the flu strains. Vaccines can typically protect against three or four types of flu virus at most.

Experts at the WHO therefore have to take a gamble on predicting which strains will become a problem that winter, based on their surveillance of emerging flu epidemics around the globe.

This year, the jab will effectively protect you from about one-third of the strains that are around. On a good year, the annual jab can protect you from just over half of them. I would heartily encourage people to have the vaccine for the protection it does confer.

The basic problem is that, currently, seasonal flu vaccines can only attack two proteins in the flu virus, which sit on its outer surface. But individual strains are constantly mutating in ways that render the vaccine useless against that strain.

We need a vaccine that attacks something fundamental in the virus that does not change, so it is effective against all strains of flu.

At least six teams around the world are trying to achieve this. Each is taking a different approach to the problem. It really is trial and error. Most of the people involved say that we are at least five to ten years away from achieving anything useful.

The good news is that the scientific community knows what needs to be done. But we are not moving fast enough, or using sufficient resources, to outrun the next big pandemic. The world’s political leaders simply do not appreciate the urgency.

We need to invest far more in producing a universal vaccine and also in ensuring that our societies are geared to protect ourselves against the inevitable next pandemic. The consequences of inaction could be catastrophic for humanity.

Dr Jonathan D. Quick is an instructor of medicine at Harvard Medical School and chair of the Global Health Council.

His book, The End of Epidemics: The Looming Threat To Humanity And How To Stop It, is published by Scribe on March 8, 2018, at £14.99.