A group of experts from the World Health Organization are set to arrive in China on Thursday for an investigation into the origins of the coronavirus pandemic.

China's National Health Commission confirmed the upcoming visit in a brief statement Monday, saying the WHO team would be meeting with Chinese scientists to conduct joint scientific research on the virus's origin. It's unclear exactly where they will be carrying out their research and whether they will travel to the central Chinese city of Wuhan, where the novel coronavirus was first detected in December 2019.

The visit follows negotiations between both sides, with WHO Director-General Tedros Adhanom Ghebreyesus expressing disappointment last week over delays with the probe.

Meanwhile, China marked one year on Monday since confirming its first death from COVID-19, the disease caused by the novel coronavirus. China's National Health Commission has since reported more than 87,000 cases of COVID-19 on the Chinese mainland, including at least 4,634 deaths, though those figures are believed to be much higher.

A new, more contagious variant of the novel coronavirus that was first detected in the United Kingdom has now been discovered in Russia.

The strain, called B117, was confirmed among four Russian citizens who had tested positive for COVID-19 upon returning from the U.K., Russia's chief sanitary doctor, Anna Popova, told reporters Sunday evening.

After being identified in Kent in September, B117 has become prevalent in London and other parts of southeast England.

Last month, Russia joined the growing list of countries to suspend flights from the U.K. amid rising COVID-19 infections and concerns about the highly infectious variant there.

With more than 3.3 million confirmed cases of COVID-19, Russia has the fourth-highest tally of diagnosed infections in the world, followed by the U.K., according to a real-time count kept by Johns Hopkins University.

Russia confirmed 23,315 new cases and 436 additional deaths from the disease on Sunday, according to the country's coronavirus headquarters.

ABC News' Alina Lobzina and Patrick Reevell contributed to this report.

Mississippi has allotted its entire supply of COVID-19 vaccines and doesn't expect more doses until mid-February, the state health department announced Wednesday.

"Neither the county health department drive-through sites, nor the [University of Mississippi Medical Center] vaccine scheduling website was designed to accommodate the monumental surge we are currently experiencing," the Mississippi State Department of Health said in a statement. "At this time, we have no additional vaccine, and every appointment is tied to an actual vaccination."

New appointments are expected to resume after an anticipated vaccine resupply in mid-February, the department said.

On Tuesday, the state opened vaccine eligibility to people ages 65 and older and those with certain chronic health conditions, which led to an influx of calls to the state's COVID-19 hotline, officials said. Previously, vaccinations were prioritized for health care workers, long-term care residents and those over the age of 75.

"We decided to open vaccines to many more people. We knew it would cause a rush, but believe it is more fair than having government arbitrarily limit access," Gov. Tate Reeves said on Twitter Wednesday evening.

As of Tuesday, the state had administered 62,744 vaccinations over the last four weeks, Reeves said during a press briefing.

ABC News' Will Gretsky contributed to this report.