An independent advisory panel of infectious disease experts, doctors and scientists recommended Thursday that the U.S. government authorize the nation's first vaccine for people over the age of 16.

It's a major milestone in the effort to get the vaccine to hospitals and pharmacies.

After hours of drilling down into data produced from a clinical trial involving 44,000 people, the group of experts -- known as the Vaccines and Related Biological Products Advisory Committee -- voted in favor of the vaccine for people over 16 years of age.

Several members raised concerns about unknowns about the vaccine, including its potential to trigger allergic reactions and little data on how it impacts pregnant women.

Several panel members also expressed concern there wasn't enough data to support giving the vaccines to 16- and 17-year-olds.

At issue was this question: "Based on the totality of scientific evidence available, do the benefits of the Pfizer-BioNTech COVID-19 Vaccine outweigh its risks for use in individuals 16 years of age and older?"

The panel voted 17-4 that the benefits outweighed the risks. One member of the committee abstained.

The U.S. Food and Drug Administration will now take the committee's input into account in issuing an emergency use authorization.

-ABC News' Anne Flaherty

Indoor dining and gyms will be suspended in Pennsylvania beginning Saturday, Gov. Tom Wolf announced.

Indoor gatherings will be limited to 10 people, he said.

Wolf announced the new restrictions one day after revealing that he tested positive for COVID-19.

Pennsylvania has over 422,000 confirmed cases and has lost at least 12,010 residents to the virus.

California reported 220 deaths on Thursday, surpassing the previous record of 219 on July 31.

With the average daily number of deaths climbing over the last month, the state's death toll now stands at 20,463.

California Gov. Gavin Newsom has ordered regions to follow a stay-at-home order if their intensive care unit capacity falls below 15%.

The San Joaquin Valley -- where capacity is at 1.9% -- and Southern California -- where capacity is at 7.7% -- are under stay-at-home orders until at least Dec. 28.

The Greater Sacramento region now meets the criteria and a stay-at-home order will go into effect Thursday night.

Just two regions, the Bay Area and Northern California, are not under stay-at-home orders.

ABC News’ Matt Fuhrman contributed to this report.

Utah teachers and school administrators will be eligible to receive COVID-19 vaccines as a part of phase one, directly after health care workers, Gov. Gary Herbert said.

Herbert said he expects teachers will be able to be vaccinated by the end of December or early January.

ABC News’ Matt Fuhrman contributed to this report.

The chief science adviser to Operation Warp Speed, the U.S. government's initiative to expedite vaccine development, said he doesn't know what vaccine-related executive order President Donald Trump is expected to sign on Tuesday.

"Frankly, I don't know and, frankly, I'm staying out of this. I can't comment," Dr. Moncef Slaoui told ABC News chief anchor George Stephanopoulos in an interview Tuesday on "Good Morning America."

When pressed on the matter, Slaoui added: "Our work is, you know, rolling. We have plans. We feel that we can deliver the vaccines as needed, so I don't exactly [know] what this order is about."

Trump is expected to discuss the order at a COVID-19 vaccine summit to be held at the White House later Tuesday, multiple White House officials told reporters during a background briefing on Monday evening. While it's not entirely clear on how exactly the order would work, the move is designed to prevent the U.S. government from shipping any vaccine doses it has purchased to aid foreign countries until all the needs within the United States are met.

White House officials also denied reports that the Trump administration turned down an offer last summer to purchase an additional 400 million doses of a COVID-19 vaccine developed by U.S. pharmaceutical giant Pfizer and its German partner BioNTech, and that the companies now may not be able to provide more of their vaccine to the United States until June 2021 because they have committed those doses to other countries.

When asked about the matter, Slaoui explained Operation Warp Speed's strategy in securing vaccine doses.

"We selected six different vaccines to build a portfolio to manage the risk that some may work and some may not work, but also to ensure that as more than one would work that we would accumulate vaccine doses from this portfolio of vaccines," he said. "If somebody came to us and said, let's buy more of this vaccine or that vaccine, no one reasonably would buy more from any one of those vaccines because we didn't know which one would work and which one may be better than the other. Once the vaccine's performance becomes known is the right time, given the strategy we've taken, to go and order more vaccine doses, which we may be doing. And frankly, the constructive thing to do if one of the suppliers has challenges producing enough vaccine doses is to roll our sleeves and help ensure that capacity can be increased."

Slaoui said he's confident the U.S. government will be getting vaccines to Americans who need them "as soon as possible" and that plans are "still on track."

"We will work with Pfizer to try and increase capacity and have those vaccines available," he said. "We have two more vaccines from J&J and AstraZeneca that will be completing their Phase 3 trials in January and most likely, I hope, be approved for use in February. We have tens of millions of doses from those vaccines, you know, participating to the volume of vaccines we need to immunize the U.S. population as we promised, all of it by the middle of the year 2021 and that's still on track."

Slaoui said Operation Warp Speed has a meeting with President-elect Joe Biden's transition team scheduled for Thursday.

"We look forward to, you know, sharing all the information and working together," he said. "Our objective has always been outside of politics and making sure we make available these vaccines for the U.S. people, and that's what we're doing."

ABC News' Ben Gittleson, John Parkinson and Eric Strauss contributed to this report.