What causes COVID-19 to change, will we see more variants and if we do will these be more infectious and/or have more severe symptoms?
Alpha, Beta, Gamma, Delta, Omicron – since SARS-CoV-2 first emerged in late 2019 the virus has evolved into many variants including the Variants of Concern (VOCs) that have predominated and are associated with severe disease and increased transmission.
According to Associate Professor Allison Imrie, a virologist and immunologist from The University of Western Australia’s School of Biomedical Sciences, coronaviruses can adapt and change very fast and often.
Omicron emerged in late 2021 and has become the dominant VOC and now a sub-variant BA.2 is causing a surge in cases. But despite seeming to be more contagious, Omicron BA.1 and BA.2 seem to cause less severe disease compared to earlier strains.
“By the time Omicron emerged much of the world has had some kind of exposure and developed immunity, either to infection or by vaccination,” Associate Professor Imrie said.
Image: Associate Professor Allison Imrie, a virologist and immunologist from UWA.
“So the question about this newest variant is, is it the existing high-level of immunity that's dampened disease severity , or is the virus intrinsically different that it causes less severe disease compared to earlier strains?”
So are more variants likely to come along and will these strains be more severe?
“We can’t say that new virulent variants are not going to emerge,” Associate Professor Imrie said. “You can speculate that you might not get this kind of disease that you saw in the previous two years because there is so much immunity but the reason some viruses get selected to become more predominant is because they can escape that immunity.
“This is a new virus and we just don't know what it is capable of doing. We've been learning a lot about it and we understand how severe the disease it causes can be, at the time of infection and also for weeks or months afterwards for some people. So that's the question: as the virus continues to evolve, will it continue to cause the relatively mild disease we’re seeing with Omicron or will more virulent viruses appear?”
Although much is still not known about COVID-19, over the past two years many resources have been directed to research to understand where the virus came from and how it has evolved.
“When the virus was first detected it had just spilled over from animals so it had to adapt to humans and we saw that process occurring in in the early months,” Associate Professor Imrie said.
The initial strain, first detected in Wuhan, continued to mutate even after it had adapted to humans, before spreading across the globe and evolving in different parts of the world.
“These viruses evolve because mistakes – mutations – are made when its genetic material is copied and then the question is why some mutations are favoured over others as the virus continues to circulate,” Associate Professor Imrie said.
There are several theories as to how SARS-CoV-2 has evolved into the VOCs that we have seen since 2020: one is cross-species transmission; another that it may mutate and diversify in people with compromised immune systems; and also that different strains that infect the same person can recombine and produce a completely new virus.
Associate Professor Imrie cited transmission between animals and humans in mink farms in Europe where virus circulating in humans was passed on to mink, then transmitted back into humans. This virus had a number of mutations not previously observed, and was less sensitive to human antibodies.
The Omicron variant was first detected in South Africa and there has been speculation that this variant may have evolved in immunocompromised people.
“Some people who don't have good immune responses – people who are being treated for cancer, transplant recipients, people who are immunocompromised because of HIV infection - their immune system is not able to control virus replication,” Associate Professor Imrie said.
“The virus changes within that immune-compromised person and the virus that is transmitted can be very different.”
Media references
Annelies Gartner (UWA Media Advisor) 08 6488 6876