Washington, Apr 9 (IANS): The United States has recorded more than 20,000 infection cases of coronavirus variants, according to the US Centers for Disease Control and Prevention (CDC).

The majority of those variants cases, 19,554 cases were caused by the variant known as B.1.1.7, which was originally detected in Britain, Xinhua news agency reported on Thursday.

There were 424 cases of a new strain initially discovered in South Africa, called B.1.351, and 434 cases of the P.1 strain first discovered in Brazil.

In addition, the B.1.427 and B.1.429 variants, two coronavirus strains first detected in the U.S. state of California, are also being closely monitored by the CDC.

The five coronavirus strains are currently classified by the CDC as "variants of concern," as evidence shows an increase in their transmissibility, increased hospitalizations or deaths, reduced effectiveness of treatments or vaccines, and diagnostic detection failures.

Even as the country picks up its Covid-19 vaccination pace, the coronavirus variants are spreading rapidly, and experts warn the variants infections could potentially stall the nation's recovery from the pandemic.

The B.1.1.7 variant is "now the most common lineage circulating in the United States," said CDC Director Rachelle Walensky on Wednesday.

"Testing remains an important strategy to rapidly identify and isolate infectious individuals, including those with variants of concern," she said.

Walensky said earlier the B.1.1.7 strain was starting to become the predominant strain in many regions of the United States, accounting for 26 percent of COVID-19 cases circulating across the nation.

She urged the public to continue pandemic safety measures, such as washing hands, wearing masks and practicing social distancing.

Walensky said the United States must accelerate its vaccination efforts.

About 174 million Covid-19 vaccine shots have been administered by Thursday, while more than 229 million Covid-19 vaccine doses have been distributed across the country.

On Tuesday, US President Joe Biden announced that all American adults will be eligible for Covid-19 vaccine by April 19, moving up his original deadline by nearly two weeks.