In its latest forecast, the University of Washington's Institute for Health Metrics and Evaluation (IHME) predicts "spring spike" in coronavirus deaths in the United States if emerging variants rapidly spread and people let down their guard against the virus.
IHME estimates the B.1.351 variant first detected in South Africa and identified in the United States this week could drive the country's Covid-19 death toll up to 654,000 by May 1 in a worst-case scenario if mobility returns to pre-pandemic levels, Xinhua news agency reported on Saturday.
A resurgence of the virus could also occur in the spring in California and Florida, according to the forecast.
Keeping mobility low and maintaining social distancing could reduce that number by approximately 30,000, said the forecast.
IHME's forecasts predict only 38 per cent of people in the United States will be immune by May 1.
In a worst-case scenario, there is also the possibility of a third wave next winter, according to the forecast.
The vaccine rollout in the United States has drawn great public attention since it started on December 14 last year. Health experts and officials have blamed states for slow vaccine rollout.
In face of growing frustration over vaccine shortages, US President Joe Biden announced earlier this week a roughly 16 per cent boost in vaccine deliveries to states over the next three weeks.
The country expects to provide enough doses to vaccinate 300 million Americans by the end of the summer or early fall, according to Biden.
About 27.88 million doses have been administered as of January 29, according to the US Centers for Disease Control and Prevention.
Meanwhile, the US Centers for Disease Control and Prevention (CDC) reported 437 cases caused by variants from more than 30 states as of Friday. The agency warned that the emerging variants may make the coronavirus cause more severe disease and spread more easily between humans.
The CDC also said on its website that some variants can spread and become predominant while others subside.
According to Xinhua news agency report, On Saturday US Covid-19 case count rose to 26,012,880, with a total of 438,239 deaths, as of 2.22 p.m. local time (1922 GMT), according to the CSSE tally,
The United States remains the nation worst hit by the pandemic, with the world's most cases and deaths, making up more than 25 per cent of the global caseload and nearly 20 per cent of the global deaths.
US Covid-19 cases reached 20 million on January 1, and have increased by six million within a month.
According to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University, the total number of Covid-19 cases in the United States has topped 26 million.
(From IANS with edits)