Six lions and three tigers at the Smithsonian's National Zoo have tested presumptive positive for the virus that causes COVID-19, the zoo said.

Last weekend the animals were observed to be coughing, sneezing, fatigued and showing decreased appetites, the zoo said. No other animals are showing symptoms.

"Given the substantial distance between the animals and visitors, the public is not at risk," the zoo said. "The Zoo has conducted a thorough investigation of all staff that were in close proximity to the lions and tigers. There is no evidence to pinpoint the source of the infection."

The animals are being treated with antibiotics for presumptive secondary bacterial pneumonia as well as anti-inflammatories and anti-nausea medication.

A vaccine made specifically for zoo animals is expected to be available in the coming months, the zoo said.

The FDA's independent advisory committee meeting is now underway to debate Pfizer's booster shots.

After a full day of presentations, Q&A and debate, the committee will vote at about 4:45 p.m. ET on whether a booster dose is safe enough for widespread use and whether it's necessary and effective at improving protection levels against COVID-19.

The vote will be non-binding. The FDA is not required to follow the advisory committee’s recommendations but generally does so. After that vote, the FDA will formally amend its current vaccine approval for Pfizer.

Next week, the matter heads to the CDC’s independent advisory panel whose members will weigh in on who should get a booster and when. The CDC Director will then formally sign off on what the panel recommends.

-ABC News' Sasha Pezenik

The most populous county in Washington state will implement COVID-19 vaccine and testing requirements for indoor dining, large outdoor events and other activities.

Starting Oct. 25, proof of COVID-19 vaccination will be required for everyone ages 12 and up to enter indoor establishments, including restaurants, bars, gyms and movie theaters, and attend outdoor events with more than 500 people in King County, home to Seattle, officials announced Thursday.

Those who are not vaccinated must show proof of a negative PCR COVID-19 test in the last 72 hours or take a rapid test on site prior to entry.

"We are at a critical point in this pandemic, with high levels of new COVID-19 cases and hospitalizations, and no certainty as to what will follow the Delta variant," King County Executive Dow Constantine said in a statement. "Vaccination is our best shield against this deadly virus."

Over 85% of King County residents have received at least their first dose of the COVID-19 vaccine, according to Constantine.

Lumen Field, home of the NFL's Seattle Seahawks, already required vaccination or a negative test, while the MLB's Seattle Mariners said last week they would institute the same guidelines should they make the playoffs.

Two dozen state attorneys general are threatening legal action against the federal government over a COVID-19 vaccine mandate for private businesses.

A week after President Joe Biden announced that the Occupational Safety and Health Administration will create a rule that will require roughly 80 million workers nationwide to be vaccinated or undergo weekly testing, 24 Republican state attorneys general warned in a letter addressed to the president that they "will seek every available legal option" if the mandate is implemented.  

The letter, which called the plan "disastrous and counterproductive" and debated its legality, was signed by the attorneys general of Alabama, Alaska, Arizona, Arkansas, Florida, Georgia, Indiana, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Montana, Nebraska, New Hampshire, North Dakota, Ohio, Oklahoma, South Carolina, South Dakota, Texas, Utah, West Virginia and Wyoming.

Earlier this week, U.S. Surgeon General Vivek Murthy defended Biden's vaccine plan in an interview with "This Week" anchor George Stephanopoulos.

"The requirements that he announced are not sweeping requirements for the entire nation," Murthy said. "These are focused on areas where the federal government has legal authority to act."