The delta variant, viewed using an electron microscope Steve Gschmeissner/Science Photo Library
WE HAVE been watching evolution in action as one coronavirus variant after another emerges and triggers further waves of infections around the world. There is every reason to think this will continue during 2022 – and there is no guarantee that future variants will be any less dangerous.
For the SARS-CoV-2 coronavirus, survival is all about infecting as many people as possible. Variants that are better at spreading will outcompete other variants. A key part of this is transmissibility. When the original virus began spreading, every infected person infected two or three others on average. Delta infects six or seven. Omicron seems to be even more contagious.
It isn’t yet fully understood how the virus is becoming more infectious. But with delta, it might be because it is better at replicating itself, meaning infected people shed more of the virus.
Infecting people is no longer as easy as it used to be, however. Most people in the world now have some degree of immunity because of past infection or vaccination. So variants such as omicron are evolving to evade this immunity, typically through changes in the outer spike protein, the main target of our antibodies.
There is a limit to how much more infectious the virus can become, but there may be no limit to its ability to evade our immune response. As happens with human flu viruses, we may see the continual emergence of new variants that evade immunity enough to cause wave after wave of infections.
“Most people around the world now have some immunity from past infection or vaccination”
It is possible that, over time, different viral lineages will persist and diverge, rather than successive variants wiping out all others and sweeping to dominance. This could require different vaccines to be combined into a single dose, as is done with the flu vaccine.
It is often claimed that new viruses will evolve to cause milder symptoms. But because SARS-CoV-2 is most infectious just before symptoms appear, there is little selective pressure for it to do this. Smallpox was highly lethal and might have become worse over time. Flu still exacts a high annual death toll.
Another concern is that the virus might be circulating in several other animals, generating new variants that could jump back into people.
While it is possible that future variants may cause more severe illness in people with no immunity, most people in the world do now have some immunity. This is likely to continue to provide some protection against severe illness even if it fails to prevent infections.
But we can expect this immunity to fade over time. Even if you have already had a booster shot, you could well find yourself standing in line to get yet another jab or two in 2022 to protect you from rho, sigma, upsilon or maybe even omega.
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