How do COVID variants emerge?

Evidence points to people with weak immune systems.

Since its first appearance in Wuhan, China, SARSCOV-2 has been acquiring random mutations. In recent months several new variants have been observed. Some of those cause significant changes in how the virus behaves, including how contagious or deadly it is.

Mutations happen all the time and are entirely random. “It’s just what viruses do,” says Gilda Tachedjian, a virologist at the Burnet Institute and president of the Australian Virology Society.

If we sequenced all the virus particles – virions – from someone infected with SARSCOV-2, we’d find that each particle is slightly different. That’s because when viruses make copies of themselves, they make mistakes. Most of these go completely unnoticed. Others confer advantages to the virus and gradually become predominant. The rapid evolution of the virus has been documented in a number of patients in the UK and US. Researchers from Cambridge University following a 70-year-old man who was immunocompromised noticed that the virus evolved rapidly after the man received plasma therapy. The virus produced “escape mutations” that helped it to evade detection by the antibodies in the plasma.

A 45-year-old Boston man undergoing immunosuppressive therapy was hospitalised with a COVID-19 infection that recurred for 154 days until he died. Rapid evolution was also reported in an immunocompromised patient who remained asymptomatic over several months.

“It comes back to that ability of the virus to replicate, to introduce mutations,” says Tachedjian, “and then to evolve so that it’s able to escape the weak immune response that immunocompromised individual might have.”