New variants of the novel coronavirus continue to be found across the U.S., as health officials increase genomic sequencing efforts to track the spread and prevalence of high contagious strains and to eventually understand their impact.

Rochelle Walensky, the new director for the Centers for Disease Control and Prevention, said U.S. sequencing of Covid-19 samples has risen significantly since she took office–from 400 a week in late January, to more than 9,000 samples during the week of Feb. 20. Working with states and private labs, the CDC hopes to increase that to 25,000 in coming weeks.

More than 1 million Covid-19 tests are conducted each day across America, according to the Covid Tracking Project.

“The increased volume of sequence information is helping us to better understand the diversity of variants circulating in the United States, where they are located, and how they are spread,” she said Wednesday at a White House Covid-19 Response Team press briefing. She added that better sequencing will also help officials understand how new variants impact vaccines’ effectiveness.

The increase in sequencing comes as new coronavirus variants are spreading in various parts of the U.S. and raising questions within the scientific community. Viruses mutate all the time—and new variants are expected of all virus strains, including the coronavirus. But what has stood out about three strains detected in the U.K., South Africa and Brazil is that they spread more easily than earlier forms, leading to more infections.

“Most mutations that occur do not cause the virus to be more infectious or deadly, but some variants have mutations that are more concerning,” said Ajay Sethi, an associate professor at the University of Wisconsin–Madison.

Public-health officials have said the variant first identified in the U.K. would become the dominant strain in the U.S. by March. The highly contagious strain, known as B.1.1.7., led to a surge in cases in the U.K., lockdowns and widespread travel restrictions. Some preliminary data and studies have suggested the variant also could be more deadly.

The South Africa variant appears to make some Covid-19 vaccines less effective and has raised concerns that people who already had the disease could get it again from the new strain.

Moderna, which has one of the two authorized vaccines in the U.S., is working on a new shot designed to better protect against the variant. A study by Pfizer found that its vaccine works against the variants identified in South Africa and the U.K.

The U.K. variant has been found in 1,881 cases in 45 states as of Thursday, according to the CDC. The South Africa variant has been found in 46 cases in 14 states, and the Covid-19 mutation from Brazil has been in five cases in four states.

Florida has the most cases of the U.K. strain, over 500, followed by Michigan at 336 and California at 204, according to the CDC.

U.S. scientists, meanwhile, are studying two domestic mutations of the virus — one specific to California, and another in New York.

In February, a study by the California Institute of Technology found the New York variant, called B.1.526, accounted for around 25% of coronavirus genomes sequenced in New York.

A study conducted by the University of California, San Francisco that has yet to be published or peer reviewed suggests the California strain is growing at a fast rate but increased transmissibility or severity of infection hasn’t been confirmed.

“For the new variants, I think it’s a bit premature to really declare what we’re seeing and this reinforces that we need more genomic sequencing and to be vigilant in our infection prevention and public health control measures while we learn more about them,” said Saskia Popescu, an assistant professor in the Biodefense Program at the Schar School of Policy and Government at George Mason University.

Still, Dr. Sethi noted that there is evidence the California and New York variants are spreading rapidly, which is a reason for concern. “More infectiousness will result in more cases, more hospitalizations, and more deaths in unvaccinated people,” he said.



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