Washington: The US has so far recorded more than 10,000 confirmed cases of coronavirus variants leading to health experts warning of another resurgence in the worst-hit country in the world.
Among the total 10,985 variant cases reported by the US Centers for Disease Control and Prevention (CDC) as of Sunday, 10,579 of them were caused by the variant known as B.1.1.7, which was originally detected in Britain late last year, reports Xinhua news agency.
There were 288 cases of a new strain initially discovered in South Africa, called B.1.351, and 118 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 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 hospitalisations or deaths, significant reduction in neutralization by antibodies generated during previous infection or vaccination, reduced effectiveness of treatments or vaccines, or diagnostic detection failures.
Experts have repeatedly expressed concern that the country would face another surge in Covid-19 cases if Americans did not keep protective measures such as wearing masks, avoiding travel, and continuing social distancing until more people are vaccinated.
Despite the drop of new Covid-19 cases, deaths and hospitalisations for weeks, now the country has seen a rise in new cases in 27 states.
Currently the seven-day average of new Covid-19 cases is about 61,000 cases a day, a 10 per cent increase over the previous period, according to the CDC.
The current seven-day average of daily new hospitalizations is about 4,816 people, a 4.2 per cent increase over the previous week, CDC data show.
CDC Director Rochelle Walensky said on Monday she feels a sense of "impending doom" about another surge in cases as infections increased by 10 per cent.
Walensky said CDC data show that new cases and hospitalisations are increasing, which she attributed to increased travel in recent weeks, lifting restrictions, and more relaxed behaviour.
"I'm going to reflect on the recurring feeling I have of impending doom. We have so much to look forward to, so much promise and potential of where we are, and so much reason for hope. But right now, I'm scared," Walensky said during a White House briefing.
Public health officials said protective measures like mask use, physical distancing, hand hygiene and prompt vaccination can help prevent against infections and emerging strains.