3 Theories to Explain Why the Mutant Coronavirus Is More Transmissible
Scientists are racing to understand why the B.1.1.7 variant spreads more easily
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The most worrying feature of the mutated coronavirus variant known as B.1.1.7 is that it’s more transmissible, meaning people infected with this variant can spread it more easily to others. Experts estimate that this strain, first identified in the U.K., is at least 50% more transmissible than the dominant strain. Last week in the Coronavirus Blog, I wrote about the different mutations identified in B.1.1.7’s genome, and what changes they might be causing in the virus itself.
Scientists are working to figure out how these mutations work in tandem to cause the variant to act differently, leading to increased transmission. Linda Saif, PhD, a virology expert and co-director of the Ohio State University Infectious Diseases Institute, explained to the Coronavirus Blog that while it isn’t yet known why B.1.1.7 and the B.1.351 variant (first identified in South Africa and also in circulation) are more transmissible, researchers have proposed several theories, all of which warrant further investigation.
One idea is that these variants bind more effectively to a key receptor on human cells. To infect a human cell, SARS-CoV-2 must latch onto a receptor known as ACE2. If the variants bind more tightly to this receptor, says Saif, it means that they can infect people more efficiently. “This includes children who generally have lower expression of ACE2 than adults,” she added. In my previous article on B.1.1.7, I discussed one mutation of note, called N501Y, that’s associated with more effective binding (known as higher affinity).
Another theory is that once a person is infected with one of these variants, the virus replicates to higher levels in the upper respiratory tract so that more of it is released, or “shed,” when a person coughs, talks, or sneezes. More shedding, says Saif, makes a virus even more transmissible.
A third proposal, she explains, is that people become infected faster after exposure to a higher dose of virus and that infected people could also shed the virus longer.
While more research is needed to show whether any of these explanations can account for the higher transmissibility of the variants in circulation, one thing that’s clear is how to prevent their spread. “These concerns may require wearing of a higher level of protective masks and staying even more than six feet apart,” says Saif. “However the good news is that early studies suggest that the current vaccines will still be effective against the variants.”
