The total number of COVID-19 cases in the United States has surpassed 50 million on Monday, while the death toll from the disease is approaching 800,000, according to data from Johns Hopkins University.

The United States remains the country worst hit by the pandemic, with the world’s most cases and deaths. The new Omicron variant has reached more than half of the U.S. states and the dominant Delta variant continues to run rampant around the nation.

Experts said the high caseload and death toll are the results of a confluence of factors: low vaccination rates, colder weather that forces more people indoors, and a still-divided political response to combatting the virus.

The rising COVID-19 cases are driven partly by the Delta and the Omicron variants which have been spreading rapidly across the United States.

The current seven-day daily average of COVID-19 cases is about 118,500, a 37-percent jump from the previous week, according to data from the U.S. Centers for Disease Control and Prevention (CDC).

The seven-day average of daily deaths is about 1,100, up 28 percent from the prior week, the CDC said.

Currently, the United States is witnessing about 7,400 new hospital admissions each day, a 16-percent increase from the previous week, the data showed.

The Omicron variant, which is possibly more contagious than the Delta variant, has been found in at least 29 U.S. states as of Monday, since the country’s first confirmed case of the Omicron COVID-19 variant was identified in the state of California on Dec. 1.

The number reflected the potentially heightened transmissibility of the Omicron strain and complexity in taming the pandemic, health experts said.

Mutations in Omicron might increase transmissibility, confer resistance to therapeutics, or partially escape infection or vaccine-induced immunity, according to the CDC.

The United States had suffered a miserable winter, with 300,000 daily COVID-19 cases reported in early January this year.