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Thursday, May 23, 2024

Emerging SARS-CoV-2 variants raise concern for the future of the pandemic

Several strains seem to be infecting people more efficiently and rapidly

Imagine walking through campus and seeing a single white crow among a flock of black ones. The next day, you see 10 white crows. On the following day, you see 500. This is how Jonathan Eisen, a professor in the department of medical microbiology and immunology, described the rapid spread of emerging SARS-CoV-2 variants worldwide. 

Dean Blumberg, the chief of pediatric infectious diseases at UC Davis Children’s Hospital, explained that the SARS-CoV-2 virus has been mutating ever since it was discovered. Eisen elaborated that the virus generates a lot of diversity even within one infected individual. When these different forms spread to other people, the virus will appear very similar to its former host but contain slight differences. Eisen explained that it is because of these differences that the virus can be traced through people as it keeps a “record” of where it has been. 

“There’s lots of diversity, and what we’re talking about here is what they’re generally calling strains,” Eisen said. “Basically what they mean is there’s collections of viruses out there that are very similar to each other, so similar to each other that we’re going to lump them all together and call them strain 11 or whatever. And then there are other strains out there that are different enough from each other that we’re going to call it strain 12 and strain 13. There are hundreds of these.”

Although there are many different versions of the SARS-CoV-2 virus, Eisen stated that most of them do not seem to be significantly biologically different from the original variant that began to circulate in December 2019. In order for the virus to spread, it must make a copy of its genome, containing roughly 30,000 nucleotides. Each time the virus creates a copy, it is likely that there may be one or two mistakes or mutations. Eisen stated that most of the time, these mutations have no effect on the biology of the virus or are rather detrimental toward its ability to spread. Yet for the recently spreading variants, this does not seem to be the case.

“What’s different here is that there’s a collection of SARS-CoV-2 viruses that are similar to each other and different from everything else—such that we’re going to call them a strain,” Eisen said. “Some of [these strains] look like they function differently and function in ways that are a little bit scary.” 

Blumberg stated that one of the main strains being widely discussed by the media is the B.1.1.7 strain, which originated in the U.K. around September 2020, according to the Centers for Disease Control (CDC). Eisen explained that when researchers in the U.K. were sequencing the SARS-CoV-2 genome and cataloging its diversity, they noticed that this particular strain had suddenly begun to increase in frequency at an alarming rate. According to the CDC website, the mutation in B.1.1.7 affects the receptor-binding domain of the spike protein and is associated with increased transmission rates. Data on the spread of B.1.1.7 in the U.S. by the CDC shows the strain has been especially widespread in California, currently with 92 identified cases.

“The spike protein serves as the area of attachment to our human cells,” Blumberg said. “So some of these mutations allow the spike protein to bind more tightly to our cellular receptors or to get inside of our cells faster. That means they might have the ability to spread more quickly.”

While this particular strain doesn’t seem to worsen the severity of COVID-19 symptoms in infected individuals, another emerging strain raises this concern: the B.1.351 strain. First identified in South Africa, this variant contains multiple mutations in the spike protein, according to the CDC. Eisen expressed concern that the B.1.351 strain appears to make individuals sicker in some cases. Blumberg added that because of the E484K mutation, one of the mutations of the spike protein, this strain may be neutralized more weakly, potentially affecting the vaccine’s efficacy. 

“If the virus changes too much, then people who’ve already been infected, they may not have immunity and they may be susceptible,” Blumberg said. “And if it changes far enough away from the vaccine, then people who are vaccinated may not be as protected, and so that would end up prolonging the pandemic.”

Though it is not yet known what caused these sudden changes to the virus’ genome, Eisen stated that one theory attributes an accumulation of differences in between transmissions to the evolution of the virus causing rapid transmission, but this is yet to be proven. Eisen likened these strains to branches of a family tree to explain the effects of these changes.

“You have these different branches of the family tree, and most of the time, those branches are roughly similar to each other,” Eisen said. “But every once in a while, some key changes happen in the virus on those branches, and now, that whole branch—everything that descends from that individual—is now going to work differently.”

Eisen explained that his three main concerns regarding these strains are how they will respond to vaccines, testing methods and drugs. Although recent research suggests that the current vaccines will still work against the B.1.1.7 strain, Eisen is almost certain that future variants may raise issues about the vaccine and concerns of the virus developing resilience toward drugs. Eisen’s laboratory is currently working toward increasing screening of different variants to prepare for such situations when they arise.

“Every infectious disease that has ever existed, and will exist, evolves,” Eisen said. “This is not remotely surprising. We have to just be prepared. We have to continually monitor, and we have to anticipate that occasionally some of the strains that come up are going to be worse, at least from a human point of view.”

With strains that spread more easily, Eisen stated that it is possible that the pandemic could be temporarily worsened. He emphasized the need to be even more careful in following social distancing, masking and cleaning guidelines. 

“I think it’s a reminder that we need to double down on our current precautions,” Blumberg said. “So the social distancing, the masking will be appropriate for all of these strains, and then the more people that we can get vaccinated and immune that way, that’ll mean less multiplication of the virus and less development of these new variants.”
Written by: Michelle Wong —science@theaggie.org


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