The spread of the mutated SARS-CoV-2 variant known as B.1.1.7 is worrying because it’s more transmissible. This means that this strain can be spread more easily from one person to the other than the dominant strain. By one estimate, B.1.1.7, which emerged in the U.K., can be up to 70% more transmissible, though several experts agree that 50% is more likely. Though it doesn’t cause more severe disease, its increased transmissibility threatens to cause a rise in new cases and an uptick in deaths, and it may become the dominant variant as soon as March.
As scientists work to understand the new variant, one thing they’re focusing on is what actually makes it more transmissible. The Centers for Disease Control and Prevention (CDC) says that the variant is transmitted more efficiently and rapidly. But what does that say about the virus particle itself? What is it doing differently?
B.1.1.7’s genome carries a total of 23 mutations, 17 of which are in parts of the genome that could cause the virus particle itself to differ in meaningful ways. (Quick refresher: A genome carries instructions for making the proteins that ultimately make up the virus.) As Kai Kupferschmidt wrote in a thorough overview of the new variant’s mutations in Science, eight of those mutations occur in the gene that encodes the spike protein, which is critical for the virus to get into human cells. Researchers from Covid-19 Genomics UK Consortium characterized the new variant in a report on the academic forum Virological.org in December, noting three mutations in the spike protein that were of particular concern.
The N501Y mutation
First is a mutation known as N501Y. It causes a change in the spike protein’s receptor binding domain, the part that latches onto the human cell’s receptors in order to get in. In previous research, this change caused it to latch on more tightly — a characteristic known as affinity. In research on mice, this mutation has also been linked to increased infectivity and virulence. A Public Health England briefing on the new variant notes: “The most unusual and concerning single mutation in this cluster is N501Y.” Experts have noted that this mutation has appeared in…