China CDC: The wolf is coming – Deltacron is a “Grey Rhino” event.
According to our preliminary analysis on the first “Deltacron” genome, recombination event only occurs in S gene. However, recombination events involving all types of genes encoded by CoVs have been found in nature. Consequently, the genetic recombination events involving other genes and/or the combination of other genes would also occur with high probability.
Before the emergence of “Deltacron,” most scientific efforts were focused on assessing and responding to the effects of point mutations in the genome of SARS-CoV-2 during its global spread and evolution. Until now, 5 types of SARS-CoV-2 VOCs had been found circulating globally (Alpha, Beta, Gamma, Delta, and Omicron). They all exhibited increased transmissibility and varying degrees of immune escape.
Although the emergence and subsequent spread of these VOCs has had a huge impact on global health and economy, it may not have been the worst case until now, as recombination (a major mechanism bringing genetic diversity to coronaviruses) has not really emerged on a large scale and shown its power before the emergence of “Deltacron.” The emergence of “Deltacron” is therefore a “grey rhino” rather than “black swan” event.
Deltacron Is Just the Beginning
With the advent of “Deltacron,” further concerns are coming. According to our preliminary analysis on the first “Deltacron” genome, recombination event only occurs in S gene. However, recombination events involving all types of genes encoded by CoVs have been found in nature. Consequently, the genetic recombination events involving other genes and/or the combination of other genes would also occur with high probability. Furthermore, the genetic recombination event of “Deltacron” occurs at the inter-lineage level, that is the parents of the “Deltacron” came from different lineages of the same species (AY.4 and BA.1), respectively.
We could speculate that cross-species recombination events would be also appeared in future for the following reasons.
First, the variety of host types of CoVs has resulted in its wide distribution throughout the world and SARS-CoV-2 has spread all over the world.
Second, several species of mammals other than humans have been infected by SARS-CoV-2 in nature, and many more species have been shown to be susceptible to SARS-CoV-2.
In addition, the spillover events of SARS-CoV-2 between humans and animals in both directions (for example transmission of SARS-CoV-2 from humans to minks and then back to humans and further community transmission) have been found in nature.
Taken together, the probability of co-infection with SARS-CoV-2 and other types of CoVs or even other viruses in a single host would be high, leading to the occurrence of cross-species recombination with high probability. Therefore, it is difficult to predict which viral species SARS-CoV-2 will recombine with, and on which genes future recombination will occur. This kind of uncertainty is doomed to increase the likelihood of generating a novel recombinant virus with unknown risk to humans.
** So what is a Grey Rhino event?**
“A gray rhino event (or grey rhino event in British English) is a highly probable, high impact yet neglected threat: kin to both the elephant in the room and the improbable and unforeseeable black swan. Gray rhinos are not random surprises, but occur after a series of warnings and visible evidence.”