In a typical year, scientists discover two or three viruses that have never been seen in people before. The number fluctuates, but the trend has been fairly steady since the 1960s.

Most of these viruses attract little attention, and my colleagues and I have often had to search through old medical papers to find any mention of them. Some viruses disappear entirely and are all but forgotten. At the other extreme, the discovery of HIV-1 in 1983 and Sars-CoV-2 in 2020 presaged the Aids and COVID pandemics, respectively. Both have killed tens of millions.

The next time a scientist finds an unusual or unknown virus in a patient – probably in the next few months – how will they know whether it could lead to a public health emergency on the same scale as Aids or COVID? My team at the University of Edinburgh has been using the lessons of virus history to help answer this question.

Pandemics come in many forms, but in recent times the biggest culprits have been viruses with genomes made from RNA (rather than the more familiar DNA). Thousands of RNA virus species have been identified, and there may be millions, but only 239 infect humans. We recently published a catalogue that helps pinpoint the riskiest........

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