New COVID variants: what’s driving the virus to evolve, and what we can do about it
The rampant spread of COVID-19 and concern about potentially more transmissible variants of the virus from the U.K. and South Africa has scientists concerned about whether or not vaccines will hold up against these strains.
“Once more people are vaccinated, there will be potentially a selection pressure on the virus to evolve antigenically, meaning that we could see variants emerge that are more capable of evading immune responses induced by vaccination,” said Angela Rasmussen, a virologist at Georgetown University’s Center for Global Health Science and Security.
She said she’s not surprised to see more transmissible variants arise because viruses mutate all the time. Every time the virus replicates, or reproduces itself, there is a small chance an error — a mutation — can be introduced into its genome. If one or a combination of those mutations gives the virus the ability to spread more easily, that variant can out-compete other versions of the virus to become the dominant version spreading in the human population.
The U.K. variant contains 23 mutations and the South African variant has at least 21 mutations, with some overlap between the two.
She said experiments are in progress right now to determine whether one of these mutations — or perhaps a combination of them — may be driving increased transmissibility. Researchers are investigating whether the virus has acquired the ability to bind more strongly to cells, allowing it to invade more easily, or perhaps gained the ability to replicate more efficiently.
But a big concern, especially as countries around the world have started rolling out vaccines, is that these mutations might render vaccines less effective.
“The South African variant does have a mutation that is associated with some antibody escape, but it doesn’t appear that it’s total,” Rasmussen told Quirks & Quarks host Bob McDonald.
An early study suggests the Pfizer-BioNTech vaccine does appear to work against the new variants. Other vaccines are currently being tested.
Natural immunity selection pressure
That kind of “antibody escape” does seem to be possible, at least in laboratory experiments. In one study that has yet to be peer-reviewed, scientists looked at how earlier versions of the SARS-CoV-2 virus fared after repeated exposures to antibodies taken from infected patients.
The antibodies that at first had been able to take out the virus eventually stopped working as the experimental viruses developed a mutation similar to the one that’s currently a concern in the South African variant.
In another pre-print study, scientists described a 45-year-old patient who — five months later — had been reinfected with a variant that contained the mutation, and whose second infection was more severe.
Rasmussen said there’s also evidence that suggests other related kinds of coronaviruses have, in the past, been able to evolve to escape antibody response, suggesting SARS-CoV-2 might also have that capacity.
“That work has largely been done with common cold coronaviruses and looking at those over a period of decades and seeing that people are getting reinfected with novel variants that emerge to evade that population level antibody response,” she added.
Vaccine selection pressure
The real risk, according to Rasmussen, is that the enormous spread of the virus is giving it a massive number of opportunities to mutate, and potentially adapt to avoid vaccine-granted immunity, or the natural immunity acquired by those who have already been infected.
Rasmussen said she’s especially concerned about the virus’s ability to evade our immune response if countries decide to tinker with prescribed vaccine dosing regimens as a way to extend vaccine supplies.
“That could lead people to have levels of antibodies that would be sort of in the sweet spot: they would not be high enough to completely neutralize the virus or prevent infection, which would allow the virus to replicate and potentially evolve variants that would be able to evade those antibodies,” she explained.
At the moment, it doesn’t appear as though the mutations in the U.K. or South African variants would allow it to evade the immune response from fully vaccinated individuals, but that doesn’t mean it can’t happen.
“We have to have plans in place to adjust those vaccines if necessary,” she cautioned.
Variants not more virulent
One silver lining with the new variants that are emerging is that so far, none of them appear to make the virus more pathogenic, or likely to cause serious illness or death.
Viruses may often evolve to be less deadly if that facilitates their spread. Very ill or dead people are, after, all, less effective vectors for viruses. “That way they’re hitting a sweet spot which is infecting a lot of different hosts, making a lot of new viruses, but not killing the host in the course of doing that,” Rasmussen said.
But she cautions that occasionally, a mutation can incidentally affect some aspect of the immune system that can result in more serious disease.
An example is HIV where some mutant strains — if left untreated — will lead to a much more rapid progression to AIDS than others.
But, Rasmussen said, the key to getting ahead of these variants is to follow the vaccine dosing regimen, get people fully vaccinated as quickly as possible, and to take necessary measures to reduce transmission. This will reduce the opportunities for the virus to generate new mutations and find ways around our defences.