Moderator Susan Page posed the first question to Harris, revealing the first of nine topics: The coronavirus pandemic.

Noting the president's recent diagnosis, Page asked Harris, "What would a Biden administration do in January and February that a Trump administration wouldn't do?"

True to her form as a prosecutor, Harris -- the first Black woman and first Indian American to take a vice presidential debate stage -- laid out her facts, arguing the administration knew about the threat of the virus in January but didn't act soon enough.

"They were informed that it's lethal in consequence, that it's airborne, that it will affect young people," Harris said. "They knew what was happening and they didn't tell you."

Harris then said the Trump administration still doesn't have a plan.

"Well, Joe Biden does and our plan is about what we need to do around a national strategy for contact tracing, for testing, for administration of the vaccine, and making sure that it will be free for all," she said.

There was no handshake between candidates -- customary at the top of such events -- due to COVID-19 precautions. The audience, limited to under 100 attendees, applauded Pence and Harris as they took the stage.

Former Democratic 2020 presidential candidate Pete Buttigieg, who played Pence at some mock debate rehearsals for Harris, was also spotted in the audience.

Pence and Harris have taken the stage in Salt Lake City for the vice presidential debate. The candidates skipped the traditional handshake due to COVID-19 and are divided by plexiglass.

Harris' chief of staff Karine Jean-Pierre told ABC News Chief Anchor George Stephanopoulos that Harris won't spend the night fact-checking Pence on stage.

Instead, the former prosecutor will "bring the case forward" on how Biden and Harris could lead to a different America.

"This debate is about Donald Trump's failure to contain COVID-19, and not just that but to also help working families," said Jean-Pierre, adding Harris has a "very diverse team" that has prepared her for the debate.

Jean-Pierre also criticized the example Trump has set since testing positive for the novel coronavirus last week.

"You have a president right now when he left the White House, he decided that he was going to make a campaign by removing his mask. His rhetoric has been incredibly dangerous," she said. "As Joe Biden said, it's a tragedy that he believes that he was blessed to have this virus, when people are suffering."

Marc Short, Pence's chief of staff, noted that Harris, like Pence, is "also a very skilled debater and has a record as a prosecutor, so I think it will be a very engaging conversation for the American people and hopefully one that shows a clear contrast in visions between the two campaigns."

Short said Pence will argue the case that the Trump administration protected more American lives in its COVID-19 response.

With less than a month to go until the election, early voting has already begun in 33 states and at least 5.5 million votes have been cast -- hitting record numbers across the nation.

According to the United States Elections Project, spearheaded by the University of Florida's political expert, Michael McDonald, an unprecedented 5,618,155 voters have already voted and at least 69,786,179 ballots have been requested in early voting states.

The coronavirus pandemic plays a factor in explaining the large early voting numbers as well as an increase in voter interest. Voters in 2020 are more eager to cast a ballot ahead of Election Day where polling sites could be viewed as overcrowded during pandemic standards.

Seven states --- California, Colorado, Hawaii, Nevada, Oregon, Utah and Washington -- have an all-mail ballot election meaning anyone registered to vote automatically receives a ballot to their registered address.

-ABC News' Kelsey Walsh

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