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The Covid pandemic has proved to be the deadliest viral outbreak the world has seen for more than a century – so it is tempting to hope we will be spared another such crisis in our lifetimes.
But scientists have crunched the numbers – and it's bad news for anyone who is in their early 20s or younger.
A team of US and Italian researchers have calculated that a major epidemic on a scale similar to Covid is due within the next 59 years – by 2080 at the latest.
It means that, based on average UK life expectancy, anyone under 24 will almost certainly have to live through another huge health disaster. The researchers warned it could happen far sooner than that.
"When a 100-year flood occurs today, one may erroneously presume that one can afford to wait another 100 years before experiencing another such event," said Dr Gabriel Katul, professor of hydrology and micrometeorology at Duke University in the US. "This impression is false. One can get another 100-year flood next year."
Researchers looked back at the new disease outbreaks over the past 400 years and found that epidemics are not as rare as first thought.
The study looked at the scale and frequency of disease outbreaks going back to 1600, including plague, smallpox, cholera, typhus and novel influenza viruses, and found patterns that give hints about when a similar-scale event will happen again.
Modelling shows the probability of a pandemic with similar impact to Covid in any given year is about two per cent, meaning someone born in the year 2000 had about 38 per cent chance of experiencing one by now.
However, a pandemic as deadly as Spanish Flu – which killed more than 30 million people between 1918 and 1920 – is only likely to occur within the next 400 years.
Worryingly, the rate at which they appear is speeding up, meaning that the probability of living through one is growing, the authors found.
Based on the increasing rate at which novel pathogens such as Sars, Mers and Covid have broken loose in human populations in the past 50 years, the study estimates that the probability of outbreaks is likely to grow three-fold in the next few decades.
Population growth, changes in food systems, environmental degradation and more frequent contact between humans and disease-harbouring animals have all increased the risk, the authors warn.
With this growing risk factor, the researchers estimate that a pandemic similar in scale to Covid is likely within a span of 59 years. They also calculated the probability of a pandemic capable of eliminating all human life, finding it statistically likely within the next 12,000 years.
The team said worldwide Covid pandemic deaths are running at around 2.5 million a year but warned that the death toll in a future pandemic of the same scale could be eight times as bad if interventions such as contact tracing and quarantines were not enacted.
They called for more to be done to anticipate future outbreaks and prepare for large scale epidemics capable of killing millions of people.
"The most important takeaway is that large pandemics like Covid-19 and the Spanish flu are relatively likely," said Dr William Pan, associate professor of global environmental health at Duke.
"This points to the importance of early response to disease outbreaks and building capacity for pandemic surveillance at the local and global scales, as well as for setting a research agenda for understanding why large outbreaks are becoming more common.
"Understanding that pandemics aren't so rare should raise the priority of efforts to prevent and control them in the future."
The results were published in the Proceedings of the National Academy of Sciences.