Over 470 infection cases of coronavirus variants have been reported in at least 32 US states as of Sunday, according to the latest data of the US Centers for Disease Control and Prevention (CDC).
The vast majority of these cases, 467, are caused by the variant known as B.1.1.7, which was originally detected in Britain.
There are three cases of a new strain initially discovered in South Africa, called B.1.351, and one case of the P.1 strain first discovered in Brazil.
These cases identified are based on a sampling of SARS-CoV-2-positive specimens, and do not represent the total number of coronavirus variant cases that may be circulating in the United States, said the CDC.
The number may not match numbers reported by states, territories, tribes, and local officials, the CDC cautioned.
Health experts are concerned that new coronavirus strains may increase case rates to record heights if the national Covid-19 vaccine rollout faces challenges.
January has been by far the deadliest month of the pandemic in the country, with over 95,000 Covid-19 deaths, surpassing December's total of over 77,000 deaths, according to Johns Hopkins University.
The Joe Biden administration announced on Monday a 230-million-US-dollar deal to ramp up production of the country's first over-the-counter, at-home Covid-19 test.
"These are over-the-counter, self-performed test kits that can detect COVID with roughly 95 percent accuracy within 15 minutes," Andy Slavitt, White House senior adviser for Covid-19 response, told reporters.
In December, the US Food and Drug Administration authorised Australian company Ellume's Covid-19 test for emergency use. This antigen test, sold over-the-counter, can be done at home using a nasal swab, dropper and processing fluid.
The United States has recorded more than 26.21 million Covid-19 cases with over 441,700 related deaths as of Monday afternoon, according to the real-time count kept by Johns Hopkins University.