The U.K. variant of the coronavirus could become the predominant strain in the United States by March, according to a report from the Centers for Disease Control and Prevention published Friday.
So far, only 76 cases of the variant, called B.1.1.7, have been identified in the country, in 10 states, the CDC said.
But the latest research, which takes into account detailed analyses of scenarios that match the current trajectories of Covid-19 cases, projects that the variant could see "rapid growth" in coming months, putting further strain on the health care system.
"We are very concerned about this variant," said Michael Johansson, one of the study's authors and co-lead of the modeling team for the CDC's Covid-19 response.
Johansson cited evidence from the U.K. that the variant may spread from person to person more readily, and noted the CDC is working to increase efforts to do more testing for such variants in the U.S.
The CDC report comes as the U.S. continues to see cases surpass 200,000 each day. Thursday was the third consecutive day that more than 3,000 people died of Covid-19 in the United States, with a daily total of 3,957. Hospital systems across the country are overwhelmed with Covid-19 patients.
There is no evidence to suggest that the U.K. variant might make people sicker. But a faster spread is sure to lead to more cases overall, the study authors wrote, "exacerbating the burden on an already strained health care system, and resulting in more deaths."
The Spike N501Y Mutation Scientists suspect that one mutation, called N501Y, is very important in making B.1.1.7 coronaviruses more contagious. The mutation’s name refers to the nature of its change: the 501st amino acid in the spike protein switched from N (asparagine) to Y (tyrosine).
The N501Y mutation changes an amino acid near the top of each spike protein, where it makes contact with a special receptor on human cells.
Because spike proteins form sets of three, the mutation appears in three places on the spike tip:
In a typical coronavirus, the tip of the spike protein is like an ill-fitting puzzle piece. It can latch onto human cells, but the fit is so loose that the virus often falls away and fails to infect the cell.
The N501Y mutation seems to refine the shape of the puzzle piece, allowing a tighter fit and increasing the chance of a successful infection.
Researchers think the N501Y mutation has evolved independently in many different coronavirus lineages. In addition to the B.1.1.7 lineage, it has been identified in variants from Australia, Brazil, Denmark, Japan, the Netherlands, South Africa, Wales, Illinois, Louisiana, Ohio and Texas.
In addition to N501Y, the B.1.1.7 has 16 other mutations that might benefit the virus in other ways. It’s also possible that they might be neutral mutations, which have no effect one way or the other. They may simply be passed down from generation to generation like old baggage. Scientists are running experiments to find out which is the case for each mutation.
One mysterious mutation in the B.1.1.7 lineage deletes the 69th and 70th amino acids in the spike protein. Experiments have shown that this deletion enables the coronavirus to infect cells more successfully. It’s possible that it changes the shape of the spike protein in a way that makes it harder for antibodies to attach.
Researchers call this a recurrent deletion region because the same part of the genome has been repeatedly deleted in different lineages of coronaviruses. The H69–V70 deletion also occurred in a variant that infected millions of mink in Denmark and other countries. Scientists are beginning to identify a number of these regions, which may play an important role in the virus’s future evolution. www.biorxiv.org/content/10.1101/2020.11.19.389916v1
The Spike Y144/145 Deletion
In another recurrent deletion region, a number of coronavirus lineages are missing either the 144th or 145th amino acid in the spike protein. The name of the mutation comes from the two tyrosines (Y) that are normally in those positions in the protein.
Like the H69–V70 deletion, Y144/145 occurs on the edge of the spike tip. It may also make it harder for antibodies to stick to the coronavirus.
This mutation changes an amino acid from P to H on the stem of the coronavirus spike:
When spike proteins are assembled on the surface of a coronavirus, they’re not yet ready to attach to a cell. A human enzyme must first cut apart a section of the spike stem. The P681H mutation may make it easier for the enzyme to reach the site where it needs to make its cut.
Like N501Y, the P681H mutation has arisen in other coronavirus lineages besides B.1.1.7. But it’s rare for one lineage to carry both mutations.