Experts have warned of the potential risks of emerging highly transmissible COVID-19 variants as the United States reached the grim milestone of 600,000 coronavirus deaths on Tuesday.
The milestone is a sobering reminder that hundreds of Americans are still dying each day even as the nation begins to enter its "new normal", said an ABC report.
With the nationwide case count topping 33.4 million, the death toll across the United States rose to 600,012 as of 12:22 p.m. local time (1622 GMT), according to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University.
California topped the national death toll list, standing at 63,191. New York reported the country's second largest deaths of 53,558, followed by Texas with 51,940 deaths and Florida with 37,265 deaths, the CSSE tally showed.
The milestone came as more U.S. states are on their ways to full reopening. New York and California dropped nearly all COVID-19 restrictions on Tuesday.
According to the new health order released by the California Department of Public Health, almost all industry and business sectors may return to usual operations with no capacity limits or physical distancing requirements. Masks are no longer required for fully vaccinated individuals in most public settings.
Along with the vaccination rollout nationwide, the United States has witnessed continuous drops of new infections, deaths and hospitalizations since the peak in January, according to data of the U.S. Centers for Disease Control and Prevention (CDC).
Zhang Zuofeng, professor of epidemiology and associate dean for research with the School of Public Health at the University of California, Los Angeles, told Xinhua that both the incidence and mortality rates of COVID-19 have dropped over 90 percent compared with those in January this year.
As vaccination rates continue to rise, the growth rates of new infections and deaths will continue to decrease, he said.
About 43.9 percent of the U.S. population have been fully vaccinated against COVID-19 as of Tuesday, and 52.6 percent of the population has received at least one dose, according to data of the CDC.
U.S. President Joe Biden has set a national goal to have 70 percent of the U.S. population get at least one shot by the July 4 holiday.
But the goal is expected to fall short as COVID-19 vaccination rates decrease from spring highs, said a CNN report.
Less than half of adults living in Alabama, Louisiana, Mississippi, Tennessee and Wyoming have received one dose of COVID-19 vaccine, according to CDC data.
The loosening of restrictions and decreasing of vaccination rates may leave some areas vulnerable to potential pandemic hotspots and risking the progress the nation has made.
Experts are concerned that the Delta variant, which was first discovered in India, is on track to become a dominant strain of coronavirus in the United States.
The Delta variant, known by the scientific name B.1.617.2, has spread from where it was first discovered in India to over 60 countries, according to the World Health Organization.
This variant is highly transmissible, greater than the Alpha variant which is currently the dominant strain in the United States, Zhang told Xinhua. It may be associated with an increased disease severity, such as hospitalization risk, compared to Alpha, he added.
Scott Gottlieb, former commissioner of the U.S. Food and Drug Administration, said the Delta variant could lead to new outbreaks in the fall, with unvaccinated Americans being the most at risk.
The CDC has elevated the Delta variant from "variant of interest" to "variants of concern".
Zhang urged more people to get vaccinated as soon as possible to keep the variant from taking hold. He also stressed the importance of keeping social distance, wearing masks and personal hygiene as vaccines could not offer 100 percent protection.