Highly infectious UK Covid-19 strain was probably spreading in US weeks before England detected it: Study
A new coronavirus variant called B.1.1.7, which has emerged with an unusually large number of mutations and was first discovered in the UK, may have been circulating in the US since November 2020, according to scientists. This is several weeks before health officials in Britain flagged it as a concern.
In mid-December last year, UK Health Secretary Matt Hancock informed that the new Covid-19 variant, which may be associated with the faster spread in the southeastern part of England, has been identified. However, in a new analysis, researchers from the Department of Ecology and Evolutionary Biology at the University of Arizona traced the strain and found that clusters of it had emerged in California by November 6 and Florida by November 23.
“The first evidence of this lineage in the US was reported in Colorado on December 29, 2020. For the two largest clades of B.1.1.7 in the US, we infer separate introductions of B.1.1.7 into California and Florida, with median TMRCAs (time of the most recent common ancestors) of November 6 and November 23, respectively. It is striking that this lineage may already have been established in the US for some 5-6 weeks before B.1.1.7 was first identified as a variant of concern in the UK in mid-December,” write authors in the study titled, “Phylogenetic evidence that B.1.1.7 has been circulating in the United States since early- to mid-November.”
The team emphasizes that it may have been circulating in the US for close to 2 months before it was first detected on December 29. “It is also worth noting the vast majority (more than 90%) of US B.1.1.7 cases appear to be generated in these well-established domestic outbreaks rather than via travel-related introductions from the UK or other affected countries, though such cases are surely also happening,” they add.
The report, which is yet to be peer-reviewed, has been published online on virological.org. These results, suggest authors, highlight the importance of a global perspective on genome sequencing to detect and monitor new SARS-CoV-2 variants. “Given how rapidly new variants can spread across the globe due to air travel, and how long even variants with reportedly increased transmission rates can remain undetected after becoming established in new regions, it is essential that all countries continue efforts to reduce transmission,” they recommend.
The study, however, indicates that just 0.4% of coronavirus cases recorded in California between December 27 and January 2 were found to be the new variant. “This suggests the dynamics of B.1.1.7 might be somewhat less explosive in California versus its original epicenter in England, with a similar population of 55 million compared to California’s 39 million: when England was at a comparable point into its B.1.1.7 outbreak, B.1.1.7 accounted for approximately 1.2% of SARS-CoV-2 cases,” they explain.
Florida, on the other hand, accounted for 0.7% of coronavirus cases roughly a month after it first emerged in the state. “Since only 17 of 21 (81%) of Florida B.1.1.7 genomes fall into clade 1, we can further estimate that clade 1 accounted for approximately 0.6% of all SARS-CoV-2 cases in Florida as of December 27 through January 2,” the findings state. At a comparable point into the B.1.1.7 outbreak in England, B.1.1.7 accounted for about 0.1% of all cases there.
“Hence, while it is evidently younger than the California clade 1 lineage, the Florida clade 2 lineage already accounts for a larger proportion of the Florida SARS-CoV-2 epidemic than clade 1 does of the California SARS-CoV-2 outbreak,” emphasize experts.
The B.1.1.7 variant was first detected in September 2020 and is now highly prevalent in London and southeast England. It has since been identified in numerous countries around the world, including the US and Canada. According to the US Centers for Disease Control and Prevention (CDC), this variant spreads more easily and quickly than other variants. But currently, there is no evidence that it causes more severe illness or increased risk of death. However, experts have cautioned that an increase in the number of cases will put more strain on health care resources, lead to more hospitalizations, and potentially more deaths.
The agency reports that as of January 20, 144 cases of the B.1.1.7 lineage have been detected in the US. But the CDC warns that cases identified so far are based on a sampling of SARS-CoV-2-positive specimens and do not represent the total number of B.1.1.7 lineage cases that may be circulating in the US and may not match numbers reported by states, territories, tribes, and local officials.
Currently, it is not clear why the “pace of replacement of non-B.1.1.7 viruses” might be different in California, Florida, and England, but the investigators have speculated on a few possibilities that they say need to be monitored as more data become available.
“One possibility is that B.1.1.7’s transmission advantage may vary with mitigation intensity. Perhaps this lineage of SARS-CoV-2, with demonstrably higher viral loads in the upper airway than other variants, is able to seed superspreader events with relative ease when mitigation efforts are comparatively lax, but its transmission advantage is less acute when the playing field is leveled by, for example, widespread mask use and indoor crowd avoidance,” suggest scientists.
Another possibility is that the non-B.1.1.7 lineages circulating in the US, particularly in California, maybe more transmissible than the non-B.1.1.7 lineages in England with which B.1.1.7 has been competing, giving B.1.1.7 less of a “transmission advantage and, thus, a slower displacement rate of non-B.1.1.7 lineages.” “An example of this might be a new variant with the Spike RBD mutation L452R that was recently described in the press in California15. However, we caution that these preliminary estimates may be very noisy; it will be important to reassess these early apparent trends with additional time points as these outbreaks progress,” says the team.