A more contagious variant of the coronavirus, first found in the UK, is spreading rapidly in the US, doubling about every 10 days, according to a new study.

A team of researchers analyzed half a million coronavirus tests and hundreds of genomes and predicted that this variant could prevail in the U.S. in a month, potentially leading to an increase in new cases and an increased risk of death.

The new study provides the first nationwide insight into 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 prevail until March if it is like the UK. The new study confirms this projected path.

“Nothing in this article is surprising, but people need to see it,” said Kristian Andersen, study co-author and virologist at the Scripps Research Institute in La Jolla, Calif. Preeminence in most locations in the United States through March. “

The team of Dr. Andersen estimated that the transfer rate of B.1.1.7 in the US is 30 to 40 percent faster than the more common variants, although those numbers could increase as more data comes in, he said. The variant has already been boosted in other countries, including Ireland, Portugal and Jordan.

“In a few months or weeks, a very serious situation could indeed develop,” said Nicholas Davies, an epidemiologist at the London School of Hygiene and Tropical Medicine who was not involved in the study. “These can be early signals that warrant an urgent investigation by health authorities.”

Dr. Davies warned that the US data is more inconsistent than that in the UK and other countries with national variant monitoring systems. Still, he found results from some parts of the United States particularly worrying. In Florida, where the new study shows that the variant is spreading particularly quickly, Dr. Davies that a new surge could come even sooner than the rest of the country.

“If these data are representative, there may be limited time to act,” he said.

Dr. Andersen and his colleagues put their study online on Sunday. It has not yet been published in a scientific journal.

When the British government announced the discovery of B.1.1.7 on December 20th, Dr. Andersen and other researchers in the US to test American coronavirus samples. The first case surfaced in Colorado on December 29th, and Dr. Andersen soon found another in San Diego. In a short time it was discovered in many other parts of the country.

However, it was difficult to determine how widespread the variant was. B.1.1.7 contains a characteristic set of 23 mutations that are scattered in a genome with 30,000 genetic letters. The best way to find out if a virus belongs to the B.1.1.7 line is to sequence its entire genome – a process that can only be done with special machines.

The CDC hired Helix, a laboratory testing company, to examine their Covid-19 samples for signs of B.1.1.7. The variant can give a negative result in one of the three tests that Helix uses to find the coronavirus. For further analysis, Helix sent these suspicious samples to Illumina to have their genomes sequenced. Last month, Helix contacted Dr. Andersen and colleagues to help analyze the data.

The team of Dr. Andersen analyzed 212 American B.1.1.7 genomes and came to the conclusion that the variant most likely first arrived in the US in late November, one month before it was detected.

Updated

Apr. 7, 2021, 3:13 p.m. ET

The variant was introduced to the country separately at least eight times, most likely due to travel from the UK to the US between Thanksgiving and Christmas.

The researchers combined data from genome sequencing with the general test results from Helix to get an estimate of the spread of the variant. It’s gotten exponentially more common in the past two months.

In Florida, scientists estimate that more than 4 percent of cases are now caused by B.1.1.7. According to his team’s calculations, the national figure can be 1 percent or 2 percent.

If that’s true, thousands or more people may become infected with the variant every day. The CDC recorded only 611 B.1.1.7 cases, confirming the inadequacy of genomic surveillance in the country.

In parts of the country where Helix doesn’t do a lot of testing, the prevalence is likely to be underestimated, warned Dr. Andersen. “I can guarantee you that there are places where B.1.1.7 has become relatively widespread and that we would not pick up,” he said.

“There’s still a lot to learn,” said Nathan Grubaugh, a virologist at Yale University who was not involved in the study. “But these things are important enough that we have to start doing things now.”

It is possible that chains of the B.1.1.7 transmission spread faster than other viruses. Or it could be that B.1.1.7 was more common in arriving travelers who started new outbreaks.

“I still think we are weeks away from really knowing how this will play out,” said Dr. Grubaugh.

The risk of contagion from B.1.1.7 makes it a threat to take seriously. Public health measures applied to other variants may not be enough to stop B.1.1.7. More cases in the United States would mean more hospital stays and potentially burden hospitals that are only now recovering from the record number of patients last month.

Dr. Davies and his colleagues from the London School of Hygiene and Tropical Medicine published an online study on Wednesday which found that the risk of death with B.1.1.7 is 35 percent higher than with other variants. The study has yet to be published in a scientific journal.

Communities can take steps to combat variants like B.1.1.7, as Dr. Grubaugh and his colleagues at Yale University recently reported in Cell. For example, health officials should reinforce the news about wearing effective masks, avoid large gatherings, and make sure indoor spaces are well ventilated.

The scientists also urged governments to require sick leave for people diagnosed with Covid-19 to stop the spread of the job. “Such measures could help significantly reduce community transmission,” wrote Dr. Grubaugh and his co-authors.

Vaccinations can also be part of the strategy to combat B.1.1.7. In Israel, where the variant is now prevalent, new cases, serious illnesses and hospitalizations in people over 65 have already decreased significantly, a group that has been given top priority in vaccines.

“What we have to do with the current vaccines is get them into as many people as possible as soon as possible,” said Dr. Andersen.

Shutting down B.1.1.7 also reduces the risk that the variant will evolve into something even worse. Researchers in the UK found samples of B.1.1.7 that had received a new mutation with the potential to make vaccines less effective. It is not clear whether these viruses will be spread. However, they show that the coronavirus still has a lot of evolutionary space to explore.

“We should expect them to show up here,” said Dr. Andersen. “Whatever was true elsewhere will be true here, and we have to take care of it.”