Why do some coronaviruses become pandemic threats when others do not?

Despite multiple spillover events and short chains of transmission on at least 4 continents, Middle East Respiratory Syndrome Coronavirus (MERS-CoV) has never triggered a pandemic. By contrast, its relative, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has, despite apparently little, if any, previous circulation in humans. Resolving the unsolved mystery of the failure of MERS-CoV to trigger a pandemic could help inform how we understand the pandemic potential of pathogens, and probing it underscores a need for a more holistic understanding of the ways in which viral genetic changes scale up to population-level transmission.

Automated summary

Despite multiple spillover events and short chains of transmission, MERS-CoV has never triggered a pandemic while its relative, SARS-CoV-2, has successfully led to a pandemic. Understanding the mystery of why MERS-CoV failed to trigger a pandemic could provide insights into the pandemic potential of pathogens.