A more contagious variant of the coronavirus first found in Britain is spreading rapidly in the United States, doubling roughly every 10 days, according to a new study.

Analyzing half a million coronavirus tests and hundreds of genomes, a team of researchers predicted that in a month this variant could become predominant in the United States, potentially bringing a surge of new cases and increased risk of death.

The new research offers the first nationwide look at the history of the variant, known as B.1.1.7, since it arrived in the United States in late 2020. Last month, the Centers for Disease Control and Prevention warned that B.1.1.7 could become predominant by March if it behaved the way it did in Britain. The new study confirms that projected path.

As of January of 2021, the highly transmissible B.1.1.7 variant of SARS-CoV-2, which was first identified in the United Kingdom (U.K.), has gained a strong foothold across the world.

Because of the sudden and rapid rise of B.1.1.7, the authors investigated the prevalence and growth dynamics of this variant in the United States (U.S.), tracking it back to its early emergence and onward local transmission, finding that the RT-qPCR testing anomaly of S gene target failure (SGTF), first observed in the U.K., was a reliable proxy for B.1.1.7 detection.

Sequencing 212 B.1.1.7 SARS-CoV-2 genomes collected from testing facilities in the U.S. from December 2020 to January 2021, they found that while the fraction of B.1.1.7 among SGTF samples varied by state, detection
of the variant increased at a logistic rate similar to those observed elsewhere, with a doubling rate of a little over a week and an increased transmission rate of 35-45%.

By performing time-aware Bayesian phylodynamic analyses, it was revealed several independent introductions of B.1.1.7 into the U.S. as early as late November 2020, with onward community transmission enabling the
variant to spread to at least 30 states as of January 2021.

The study shows that the U.S. is on a similar trajectory as other countries where B.1.1.7 rapidly became the dominant SARS-CoV-2 variant, requiring immediate and decisive action to minimize COVID-19 morbidity and mortality.

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