An international team of World Health Organization experts investigating the origins of the coronavirus pandemic said Tuesday it's "extremely unlikely" that the virus was leaked from a laboratory in the Chinese city of Wuhan.

The Wuhan Institute of Virology, which is affiliated with the government-run Chinese Academy of Sciences, has collected extensive virus samples, sparking speculations that it may have caused the original outbreak by leaking the novel coronavirus into the surrounding community. The institute has strongly rejected that possibility.

"The findings suggest that the laboratory incident hypothesis is extremely unlikely to explain the introduction of the virus into the human population," WHO food safety and animal diseases expert Peter Ben Embarek said at a joint press conference with Chinese counterparts on Tuesday. "Therefore, [it] is not in the hypotheses that we will suggest for future studies."

The WHO team, which includes experts from 10 countries, is considering several possible scenarios for how the disease was transmitted to humans, leading to a pandemic that has claimed the lives of more than 2.3 million people worldwide. Embarek said it's more likely that the virus jumped to humans from an animal.

"Our initial findings suggest that the introduction through an intermediary host species is the most likely pathway and one that will require more studies and more specific targeted research," he said.

Transmission through the trade of frozen products was also likely, Embarek added.

As part of their investigation, the WHO team has visited key locations in Wuhan, where the first cases of COVID-19 were detected in December 2019.

A cluster of initial cases has been linked to a now-closed wet market in Wuhan. But Liang Wannian, the lead Chinese envoy who is working on the probe, said the market may not be the first location of the outbreak since transmission was also happening in other areas of the city at the time.

A review of mortality data, antibody tests of blood in blood banks in Wuhan and genome sequences showed there was "no indication of the transmission of the Sars-Cov-2 in the population" prior to December 2019, according to Liang.

There was also no evidence of "large outbreaks" in Wuhan or elsewhere before December 2019, according to Embarek.

ABC News' Karson Yiu contributed to this report.

Major U.S. pharmacy chains are rolling out their COVID-19 vaccination programs this week, as part of the first phase of the Biden administration's Federal Retail Pharmacy Program for COVID-19 Vaccination.

The program is a collaboration between the federal government, states and territories, and 21 national pharmacy partners and independent pharmacy networks to increase access to COVID-19 vaccinations across the country. The federal government will send an initial shipment of 1 million doses of COVID-19 vaccines to 6,500 locations across the country on Feb. 11.

Starting Tuesday, Walgreens will begin accepting appointments for COVID-19 vaccinations as early as Friday, the company told ABC News in an exclusive announcement on "Good Morning America." Health care workers, people over the age of 65 and individuals with preexisting conditions will be prioritized.

"We're just very excited to transition from Phase 1A to this next population and offer the vaccination to the communities we serve every single day," Rina Shah, vice president of pharmacy operations at Walgreens, told ABC News.

However, the Walgreens rollout will be slow, starting in just 15 U.S. states and jurisdictions with limited vaccine doses and appointments available.

Meanwhile, CVS Pharmacy said it will begin accepting appointments on Thursday, with shots going into arms as early as Friday.

There were 89,727 new cases of COVID-19 confirmed in the United States on Monday, according to a real-time count kept by Johns Hopkins University.

It's the second straight day that the U.S. has reported under 100,000 newly confirmed infections. Monday's case count is also far less than the country's all-time high of 300,282 new cases on Jan. 2. Meanwhile, Sunday's case count of 89,581 was the lowest the U.S. has reported since Nov. 2, Johns Hopkins data shows.

An additional 1,596 fatalities from COVID-19 were registered nationwide on Monday, down from a peak of 5,085 new deaths on Feb. 4, according to Johns Hopkins data.

COVID-19 data may be skewed due to possible lags in reporting over the Martin Luther King Jr. Day holiday weekend last month as well as during storm-related closures in some northeastern states last week.

A total of 27,097,346 people in the U.S. have been diagnosed with COVID-19 since the pandemic began, and at least 465,083 have died, according to Johns Hopkins data. The cases include people from all 50 U.S. states, Washington, D.C., and other U.S. territories as well as repatriated citizens.

Much of the country was under lockdown by the end of March as the first wave of pandemic hit. By May 20, all U.S. states had begun lifting stay-at-home orders and other restrictions put in place to curb the spread of the novel coronavirus. The day-to-day increase in the country's cases then hovered around 20,000 for a couple of weeks before shooting back up over the summer.

The numbers lingered around 40,000 to 50,000 from mid-August through early October before surging again to record levels, crossing 100,000 for the first time on Nov. 4, then reaching 200,000 on Nov. 27 before topping 300,000 on Jan. 2.

So far, the U.S. Food and Drug Administration has authorized two COVID-19 vaccines for emergency use -- one developed by U.S. pharmaceutical giant Pfizer and its German partner BioNTech, and another developed by American biotechnology company Moderna and the National Institute of Allergy and Infectious Diseases. More than 42 million vaccine doses have been administered nationwide, according to the latest data from the Centers for Disease Control and Prevention.

The COVID-19 hospitalization rate in the United States continues to see a downward trend, according to data complied by The COVID Tracking Project, a volunteer-run effort to track the U.S. outbreak.

There are currently 80,055 people hospitalized with COVID-19 symptoms nationwide, the data shows. The figure peaked at around 130,000 a few weeks ago.

"The number of people currently hospitalized with COVID-19 has dropped by 21k in 10 days. In the last week, hospitalizations have decreased by 10% or more in 40 states," The COVID Tracking Project said on Twitter Monday night.