The coronavirus variant that was first identified in the UK is now spreading rapidly in the US, doubling every 10 days, according to a new study.
That means that the variant, known as B117, is growing exponentially in prevalence.
B117 made up around 2 percent of currently circulating strains in the last week of January and likely doubled to 4 percent of circulating strains 10 days later, and 10 days after that, will double to 8 percent, then 16 percent and so on.
By March it will likely be the most common variant in the country.
The variant, which seems to be about 40 percent to 70 percent more transmissible than previous forms of SARS-CoV-2, the virus causing COVID-19, has "gained a strong foothold across the world," the authors wrote in a new preprint study posted on medRxiv on February 7 and not yet peer-reviewed.
B117 has multiple mutations on its spike protein — which the virus uses to latch onto and invade human cells; those mutations seem to allow the virus to spread faster and more efficiently compared with earlier forms of the virus.
B117 was first detected in September 2020 in the UK, and just two months later, it became the dominant variant in the country. The variant has now been detected in at least 80 countries and territories across the globe, according to the World Health Organization.
After B117 showed up in Portugal and Ireland, those countries "observed devastating waves of COVID-19," the authors wrote in the new study.
"Our study shows that the US is on a similar trajectory as other countries where B117 rapidly became the dominant SARS-CoV-2 variant."
The Centers for Disease Control and Prevention (CDC) predicted that B117 would become the dominant strain in the US by March, Live Science previously reported, and unfortunately, this study suggests that prediction is coming true.
To understand how fast B117 is spreading in the US, researchers examined data from a half-million positive test samples in the US collected by genomics company Helix since July 2020. They found that B117 likely arrived in the US toward the end of November and had spread to at least 30 states by January.
They also found that while the variant is still at a "relatively low frequency," in the US, it is 35 percent to 45 percent more transmissible than earlier forms of the virus; and its prevalence appears to be doubling every 10 days across the country.
The variant was most prevalent in Florida, accounting for 4.5 percent of cases there by the last week of January. That also fits with published data from the CDC showing that most of the 690 known cases of B117 came from Florida, followed by California, according to the CDC.
That said, the data didn't cover the entire US and so variants may be circulating undetected in several states, according to the study.
Labs in the US are sequencing only a small proportion of SARS-CoV-2 samples, so many new and unknown variants may be circulating under the radar, the authors wrote.
"The more established surveillance programs in other countries have provided important warnings about variants of concern that can impact the US, with B117 representing only one variant that demonstrates the capacity for exponential growth," they wrote.
Given that B117 is still not extremely widespread in the US, there's still time to implement surveillance programs and mitigation efforts in the weeks to come, the authors wrote.
But "unless decisive and immediate public health action is taken," the spread of the variant will likely have "devastating consequences" within a few months in the US, they added.
Scientists weren't sure at first whether B117 is more deadly and more transmissible than earlier forms of the virus. Some early evidence from the UK suggests that it may be 30 percent more deadly, but that evidence is still uncertain, Live Science previously reported.
In any case, B117 is "almost certainly destined" to become the dominant strain in the US by March, the authors wrote.