DOCTORS may be fretting about concurrent outbreaks of flu and covid-19 (see “What will happen to covid-19 cases in winter and how can we prepare?” ) but some virologists are worrying about another scenario: a Frankenvirus.

SARS-CoV-2, the virus that causes covid-19, almost certainly originated from the hybridisation of two different coronaviruses. The details remain hazy, but the virus’s genome sequence suggests that this mash-up occurred in a bat about a decade ago. The bat was simultaneously infected …