As variants of SARS-CoV-2—the coronavirus that causes Covid-19—continue to spread around the world, scientists have hypothesized three key ways the virus could evolve in the future, Emily Anthes reports for the New York Times.

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Viral replication

When SARS-CoV-2 was first identified in January 2020, scientists held on to "one glimmer of hope"—the fact that coronaviruses tend to evolve slowly and be relatively stable, Anthes writes.

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"There was, I think, a sense that would work in our favor, and that the nightmare scenario of it being like influenza—constantly changing and needing updated vaccines all the time—would probably not be the case," said Adam Lauring, a virologist and infectious disease physician at the University of Michigan.

But researchers at the time did not realize the coronavirus would spread globally, Anthes writes, with more than 237 million people infected globally since the start of the pandemic, and about 4.8 million deaths worldwide. According to Anthes, every infection gave the virus a new opportunity to mutate, leaving the world with an "alphabet of new viral variants," including alpha, beta, gamma, delta, lambda, and the most recent variant, mu.

"We just have uncontrolled infections in much of the world," Lauring said, "and that's going to lead to more chances for the virus to evolve."

According to experts, the coronavirus could ultimately evolve in countless ways, but there are three concerning possibilities.

1. It could become even more transmissible

SARS-CoV-2 has already become more transmissible than it was when it first emerged, Anthes writes.

"The virus is just better at transmitting from one person to another than it was in January of 2020," Jesse Bloom, an expert in viral evolution at the Fred Hutchinson Cancer Research Center, said. "And this is due to a variety of mutations that the virus has acquired, some of which we understand and some of which we don't."

Although many experts were surprised how quickly new coronavirus variants emerged the appearance of highly transmissible variants is "textbook viral evolution," Anthes writes, since viruses do not show up perfectly formed.  

But despite the coronavirus' highly transmissible mutations, Bloom explained to Anthes that "there are likely some basic biological limits on just how infectious a particular virus can become, based on its intrinsic properties. Viruses that are well adapted to humans, such as measles and the seasonal influenza, are not constantly becoming more infectious."

As a result, while it is not completely clear what the limits of transmissibility are, Bloom pointed out that, at minimum, the coronavirus "cannot replicate infinitely fast or travel infinitely far," Anthes writes.

"Transmission requires one person to somehow exhale or cough or breathe out the virus, and it to land in someone else's airway and infect them," Bloom said. "There are just limits to that process. It's never going to be the case that I'm sitting here in my office, and I'm giving it to someone on the other side of Seattle, right?"

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But that said, he acknowledged it's unclear whether "the delta variant is already at that plateau, or whether there's going to be further increases to get that to plateau[.]"

2. It could become better at evading our immune system

In addition to increased transmissibility, Anthes writes that some variants of the coronavirus have developed the ability to dodge certain antibodies. Specifically, according to Anthes, genetic mutations in certain variants of the coronavirus can prevent antibodies from blocking the virus from entering our cells.

Currently, although delta appears to evade some of these antibodies, it is not as effective as other variants, such as beta, Anthes writes. As a result, since delta "is so infectious," it has "managed to outcompete, and thus limit the spread of, these stealthier variants," she explains.

However, as more people develop antibodies against the virus, the mutations that allow the virus to infect people will become even more advantageous. "The landscape of selection has changed," said Jessica Metcalf, an evolutionary biologist at Princeton University. "From the point of view of the virus, it's no longer, 'I just bop around, and there's a free host.'"

Thankfully, experts say that because there are many different types of antibodies, a variant with just a few new mutations will likely not be able to evade all of them. And so far, according to Shane Crotty, a virologist at the La Jolla Institute for Immunology, research indicates that our antibody, T cell, and B cell responses are all working as expected against the coronavirus.

"The immune system has also evolved to have plenty of tricks up its sleeve to counteract the evolution of the virus," said Marion Pepper, an immunologist at the University of Washington School of Medicine. "Knowing that there is this complex level of diversity in the immune system allows me to sleep better at night."

3. It could become more virulent

Experts also hypothesize that the coronavirus could become more virulent—although they admit that that this concern may be the hardest to predict because, unlike transmissibility or immune evasion, virulence has no inherent evolutionary advantage.

"The virus has no interest in killing us," Metcalf said. "Virulence only matters for the virus if it works for transmission."

Right now, it is too early to definitively say whether the coronavirus will see long-term changes in virulence, experts said. And there could potentially be trade-offs between virulence and transmission, since variants that cause serious illness and spread quickly may not spread very far.

But on the other hand, researchers have pointed out that as the coronavirus spreads before people become severely ill, it could theoretically become more virulent without giving up its transmissibility. Moreover, the mechanisms and processes that make the coronavirus more transmissible, including quicker replication or improved binding to cells, could also make it more virulent.

The coronavirus will keep evolving

Even though experts can't predict the exact viral evolution, they are certain that the coronavirus will not stop evolving—and the "arms race between the virus and us is just beginning," Anthes writes.

Currently, the Covid-19 vaccines are currently our most powerful weapon against the virus. "I think there is hope in the fact that the SARS-CoV-2 vaccines at this point are more effective than flu vaccines have probably ever been," Bloom said.

However, a large portion of the world is still unvaccinated, Anthes writes, and the coronavirus has already proven its ability to surprise us. "We should be somewhat cautious and humble about trying to predict what it is capable of doing in the future," Crotty said.  

Ultimately, while we can't predict exactly how the virus will progress, Jonathan Quick, a global health expert at Duke University and the author of "The End of Epidemics," said the future "depends much, much more on what humans do than on what the virus does." (Anthes, New York Times, 10/12)