The findings showed that the probability of a pandemic similar to the deadliest pandemic in modern history -- the Spanish flu, which killed more than 30 million people between 1918 and 1920 -- ranged from 0.3 per cent to 1.9 per cent per year over the time period studied.
The world will likely see a pandemic similar to Covid-19 within the next 60 years, say researchers stressing the need to prioritise efforts to prevent and control them.
Researchers from the Universities of Padua in Italy and Duke in the US used new statistical methods to measure the scale and frequency of disease outbreaks including a row of pathogens like plague, smallpox, cholera, typhus, and novel influenza viruses over the past 400 years to estimate the intensity of those events and the yearly probability of them recurring.
The findings showed that the probability of a pandemic similar to the deadliest pandemic in modern history -- the Spanish flu, which killed more than 30 million people between 1918 and 1920 -- ranged from 0.3 per cent to 1.9 per cent per year over the time period studied.
These figures also mean it is statistically likely that a pandemic of such extreme scale would occur within the next 400 years.
But the data, appearing in the Proceedings of the National Academy of Sciences, showed the risk of intense outbreaks is growing rapidly.
Based on the increasing rate at which novel pathogens such as SARS-CoV-2 have broken loose in human populations in the past 50 years, the study estimates that the probability of novel disease outbreaks will likely grow three-fold in the next few decades.
Using this increased risk factor, the researchers estimate that a pandemic similar in scale to Covid-19 is likely within a span of 59 years, a result, they write, is "much lower than intuitively expected".
"That is not to say we can count on a 59-year reprieve from a Covid-like pandemic, nor that we're off the hook for a calamity on the scale of the Spanish flu for another 300 years. Such events are equally probable in any year during the span," said Gabriel Katul, Professor of Hydrology and Micrometeorology at Duke.
"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," Katul said. "This impression is false. One can get another 100-year flood next year."
The reasons outbreaks are becoming more frequent are population growth, changes in food systems, environmental degradation and more frequent contact between humans and disease-harbouring animals may all be significant factors.
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