During the first open discussion session, Page asked Harris if she would take a COVID-19 vaccine if it was approved by the Trump administration.

"If the public health professionals -- if Dr. Fauci, if the doctors tell us that we should take it, I'll be the first in line to take it, absolutely," Harris said. "But if Donald Trump tells us I should take it -- that we should take it, I'm not taking it."

Page tried to move on to the next topic -- the role of the vice president -- but Pence used his uninterrupted two minutes to respond to Harris' comment on a potential vaccine and to criticize how the Obama administration handled the Swine Flu or H1N1 pandemic of 2009.

"We have five companies in phase three clinical trials and we're right now producing tens of millions of doses," the vice president said.  "So, the fact that you continue to undermine public confidence in a vaccine, if a vaccine emerges during the trump administration, I think is unconscionable."

"And senator, I just ask you, stop playing politics with peoples' lives. The reality is, that we will have a vaccine, we believe, before the end of this year," he added.

In light of the president's recent diagnosis, Page directly asked Pence, "How can you expect Americans to follow the administration's safety guidelines to protect themselves from COVID when you at the White House have not been doing so?"

"Well, the American people have demonstrated over the last eight months that, when given the facts, they're willing to put the health of their families and their neighbors and people they don't know first," Pence said.

Pence also addressed the Sept. 26 Rose Garden event during which social distancing and masks weren't enforced and after which several White House officials tested positive.

"Many of the people who were at that event, Susan, actually were tested for coronavirus, and it was an outdoor event which all of our scientists regularly and routinely advise," Pence said. "The difference here is, President Trump and I trust the American people to make choices in the best interest of their health."

Pence defended the White House's response to the COVID-19 pandemic, saying that Trump "has put the health of America first." Pence pointed to the administration's early ban on travel to China, testing efforts and the efforts to research and administer a vaccine.

Pence also went after the plan the Biden campaign released to combat coronavirus, saying "it reads an awful lot like what President Trump and I, and our task force, have been doing every step of the way."

He said that the plan "looks a little bit like plagiarism," because of its similarity to the White House Coronavirus Task Force plan.

Harris hit back at Pence, citing the revelations that Trump downplayed the coronavirus to prevent panic.

"I want to ask the American people, how calm were you when you were panicked about where you were going to get your next roll of toilet paper, how calm were you when your kids were were sent home from school? How calm were you when your children couldn't see your parents because they were afraid they could kill them?" she said.

Trump's re-election campaign is looking to have the president return the campaign trail early next week, despite his COVID-19 diagnosis last Thursday and hospital stay over the weekend.

The campaign was forced to cancel five previously announced rallies due to the president's testing positive. Multiple sources tell ABC News the Trump team has begun working to nail down details for the president's return to the campaign trail and has considered an event -- possibly in Pennsylvania -- as early as next Monday.

ABC News' Will Steakin, Katherine Faulders and John Santucci

In response to COVID-19 concerns from Kamala Harris’ team, the Commission on Presidential debates has agreed to add additional safety precautions at the debate.

Vice President Mike Pence and Harris will be seated 12-feet and 3-inches away from each other and from the debate moderator, USA Today Washington Bureau Chief Susan Page. As was the case at the presidential debate, there will be no handshakes between the candidates, and while the Commission said there would also be plexiglass separating Harris, Pence and Page, the Pence campaign has objected to using it.

A senior administration official in Pence’s office told ABC News Tuesday that there had been no formal agreement about the plexiglass and that while Harris and Page could use it, Pence doesn’t want to.

In a statement to ABC News, Pence spokeswoman Katie Miller said, "If Sen. Harris wants to use a fortress around herself, have at it."

Though Harris, Pence and Page will not wear masks on stage, everyone else in the debate hall will be required to wear one. Anyone who takes their mask off will be escorted out, according to the rules.

During the presidential debate in Cleveland, members of the Trump family were seen sitting in the audience without masks, even after being asked to put them on.

Harris and Pence will be tested prior to the debate, according to the Commission, which is a change from the presidential debate when the campaigns were responsible for testing their candidates and traveling parties.

“They’ve got to wear a mask, and if they take their mask off they're gonna be escorted out, and I don't care who they are, they'll be escorted out,” said Frank Fahrenkopf, chairman of the Commission on Presidential Debates, in an interview with ABC News.

The vice president has tested negative each day since Friday, and his White House physician has cleared him from having to quarantine, citing that he is not a “close contact” with anyone who’s tested positive, including Trump.

But Pence was present at the Rose Garden ceremony on Sept. 26 when Trump announced Judge Amy Coney Barrett as his U.S. Supreme Court nominee. Eleven of the attendees have since tested positive for COVID-19. He was also in the Oval Office with Trump the morning of his debate, just days before the president tested positive.

Harris tested negative for COVID-19 Monday after being screened in Salt Lake City, where she has been gearing up for the debate, according to an aide.

-ABC News' Justin Gomez and Averi Harper