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

ADUes:pPiteleamsuecltoipnlfeirsmptihllaotvaellrheeavdeinntgsleavnedlsasrheorretpcrhesaeinntsedocfotrrarencstmly:ission 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 (SARSCoV- 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.