In the ongoing struggle of SARS-CoV-2’s genes versus our wits, the virus that causes Covid-19 relentlessly probes human defenses with new genetic gambits. New variants of this coronavirus with increasing transmissibility have sprung up every few months, a scenario that is likely to continue.
Some experts believe that the pandemic appears to be on an evolutionary slide toward becoming endemic, a “new normal” in which humans and the virus co-exist, as we currently do with influenza. But coronaviruses are clever. While an endemic resolution may be in sight, SARS-CoV-2 could still shock the human species with a devastating evolutionary leap.
Four possible scenarios
A slide toward endemicity
Humans currently coexist with four known endemic coronaviruses. Their scientific designations sound like technical code: 229E, OC43, NL63, and HKU1. Almost every person on earth becomes infected with all four of these viruses during childhood. These infections tend to be mild, causing only transient upper respiratory infections, hence the convenient shorthand name of common cold coronaviruses (CCC) for this gang of four. Because immunity to these coronaviruses wanes with time, infections can recur throughout the human lifespan.
Altered disease and symptoms
In this scenario, SARS-CoV-2 evolves to infect new cell types in the human body, changing from predominantly infecting and affecting the respiratory system to infecting and affecting other organ systems. This scenario could lead to a better outcome or a worse one, depending on the organs damaged and the extent of it.
Emergence of a new recombinant coronavirus
There is already evidence that SARS-CoV-2 strains are recombining with other SARS-CoV-2 strains. Fowl coronaviruses and swine coronaviruses are widespread problems in commercial animal husbandry, and mouse hepatitis virus has been a common nuisance infection in laboratory mouse colonies. SARS-CoV-2-infected individuals who have close contact with coronavirus-infected animals could easily serve as hosts for the generation of recombinant viruses.
Exploitation of antibodies
In this worrisome scenario, SARS-CoV-2 evolves to not only evade its human host’s immune response but to actively exploit it. The successive major variants of SARS-CoV-2 so far — Alpha through Omicron — show that the relentless evolution of the virus helps evade the immune system. But some coronaviruses, like the feline infectious peritonitis virus, take evasion to the next level: exploitation.
The worry here is that if SARS-CoV-2 evolves to use antibody dependent enhancement to increase virus growth and transmission, the new variant could explosively retrace its spread through immune populations.