Athletes will be tested for COVID-19 at least once every four days during their stay in Tokyo at the pandemic-delayed Summer Olympic and Paralympic Games, according to a "playbook" released by organizers Tuesday.

Over the past week, Olympics organizers have released different playbooks for each group of key stakeholders that outline COVID-19 protocols and rules of conduct for before, during and after the Tokyo Games, which are slated to open July 23. The playbook released Tuesday, which is aimed at athletes and team officials, warns that individuals could be kicked out of their events if they break protocols.

In addition to regular testing at the Games, athletes and team officials must take a COVID-19 test approved by the Japanese government within 72 hours of the departure time of their flight to the country, show proof of that negative test upon arrival and be prepared to take another test at the airport. Athletes will be barred from competing at the Games if they test positive for COVID-19.

Athletes and team officials will only be permitted to leave the Olympic and Paralympic Village, or other designated accommodation, to carry out the activities detailed in their "14-day activity plan," according to the playbook. They are not allowed to visit gyms, tourist areas, shops, restaurants and bars, among other places.

The playbook also asks athletes and team officials to keep two meters away from others and avoid "unnecessary forms of physical contact such as hugs, high-fives and handshakes."

The 2020 Summer Olympics were supposed to kick off in the Japanese capital last year on July 24. But in late March, amid mounting calls to delay or cancel the upcoming Games, the International Olympic Committee and Japanese organizers announced that the event would be held a year later due to the pandemic. They have been outwardly staunch in their determination to go forward with the Games ever since, even as Japan -- and much of the world -- face a resurgence of COVD-19 infections.

Clinical trials testing a combination of Russia's flagship COVID-19 vaccine, Sputnik V, with another developed jointly by England's University of Oxford and British-Swedish pharmaceutical giant AstraZeneca will begin in Azerbaijan later this month.

The Russian Direct Investment Fund (RDIF), which funded the production of Sputnik V and is responsible for its worldwide marketing, announced Tuesday that Azerbaijan's health ministry has issued a permit to conduct the trials, which will commence before the end of February.

"The research will be carried out over the course of six months in several countries with 100 volunteers recruited in each," RDIF said in a statement.

ABC News' Alina Lobzina contributed to this report.

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.