California Attorney General Xavier Becerra, Biden's nominee to lead the Health and Human Services Department who would be the first Latino in the position if confirmed, said the incoming Biden administration will elevate the knowledge of medial professionals and build a country where health care is a right, not a privilege.

"At HHS, tackling pandemics, saving lives, keeping us healthy, should be our calling card. And we won't forget that there is a second "H" in HHS, the human services: the work we do for our children, the seniors and and disabled. They will stand tall in a Biden-Harris HHS," Becerra said.

Becerra also shared a personal story, of his father passing away peacefully at home on New Year's Day, contrasting it to the present moment.

"No one should ever have to die alone in a hospital bed, loved ones forced to stay away. That seems so contrary to the values of a great nation, the values that drew my parents like generations before and after them to come to America," he said.

Becerra led the states' defense of the Affordable Care Act after the Trump administration sued to dismantle the program earlier this year.

Ahead of introducing his health care picks, Biden made his mask campaign official and called on all Americans to wear a mask for the first 100 days of his presidency as part of three key objectives he's asking his health care team to complete in his first 100 days in office.

"My first 100 days won’t end the COVID-19 virus. I can't promise that," Biden said. "We didn’t get into this mess quickly. We're not going to get out of it quickly. It's going to take some time. But I'm absolutely convinced that in 100 days we can change the course of the disease and change life in America for the better."

Biden said his team's second initiative is to have "at least 100 million COVID vaccine shots into the arms of the American people in the first 100 days." The initiative comes as the Biden team has said it's seen "no detailed plan" on vaccine distribution from the Trump administration.

Finally, Biden said getting children back to school and keeping them in school will be a "national priority" for the team in the first 100 days, saying Congress can help make this happen with the appropriate funding.

"I'm encouraged by the bipartisan efforts in Congress around a $900 billion economic relief package which I've said is critical, but this package is only a start for more action early next year," Biden added.

Biden is introducing a slate of health care experts and officials who will lead his administration's response to the ongoing COVID-19 crisis.

"Today, I’m very proud to be announcing our health care and COVID team at a critical time, as we near the end of one of the toughest years we've faced as a nation," Biden said, adding this group of "world class experts" will be "ready on day one."

California attorney general and former California congressman, Xavier Becerra, is Biden's nominee for secretary of Health and Human Services. If confirmed, he would be the first Latino to lead the department.

Vivek Muthy has been nominated to be U.S. surgeon general, a role he served in during the Obama administration.

Dr. Rochelle Walensky, a leading expert on virus testing, prevention and treatment, is nominated to serve as director of the Centers for Disease Control and Prevention.

Dr. Marcella Nunez-Smith, one of the country’s foremost experts on health care disparities, will serve as the COVID-19 equity task force chair.

As Biden said last week, Dr. Anthony Fauci will stay on in his current role as as director of the National Institute of Allergy and Infectious Diseases and will take on the elevated role of Biden's chief medical adviser on the COVID-19 pandemic.

Jeff Zients will serve as coordinator of the COVID-19 response and counselor to the president, and Natalie Quillian will serve as deputy coordinator of the COVID-19 response.

During first speech post-election on immigration, Vice President-elect Kamala Harris’ told immigration activists that she's focused on working to “right the wrongs of these past four years."

Harris, during pre-taped remarks at the 13th Annual National Immigrant Integration Conference, ticked off a few immigration-related actions the Biden administration hopes to tackle in the first 100 days in office.

“In our first 100 days, we will send an immigration bill to Congress, reinstate DACA, repeal harmful and discriminatory policies like the Muslim ban, and during our administration, we will repeal indiscriminate enforcement policies that tear families apart and make us less safe," Harris said.

The daughter of two immigrants, Harris later noted the sacrifice that immigrants have made during the pandemic as essential workers, vowing to create a “humane immigration system.”

-ABC News' Beatrice Peterson

Trump and Biden hold dueling events on the pandemic response Tuesday with the president hosting a "vaccine summit" at the White House, just days before a Food and Drug Administration advisory committee holds a hearing on whether to authorize emergency use of a COVID-19 vaccine, while the president-elect is slated to formally roll out his health care picks who will take over handling the COVID-19 pandemic in 43 days.

At his event, Trump is slated to sign an executive order touting his mantra of "America First" that would prioritize Americans’ access to COVID-19 vaccines before the United States helps other countries. But the chief science adviser to "Operation Warp Speed," the U.S. government's initiative to expedite vaccine development which Trump is also expected to tout, said Tuesday morning he doesn't know about the vaccine-related executive order Trump is expected to sign.

"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 asked to explain the executive order.

The event comes as a senior administration official familiar with the matter confirmed reporting to ABC News that the Trump Administration passed when Pfizer offered in later summer to sell the U.S. more COVID-19 vaccine doses -- an approach which the White House has denied and Slaoui defended Tuesday. Representatives of Pfizer and Moderna -- the two drug companies seeking emergency-use authorization -- are not expected to attend the White House summit, nor is anyone from the Biden transition team.

Biden, meanwhile, is slated to introduce the health care team he will entrust with handling the pandemic California Attorney General Xavier Becerra as Health and Human Services secretary, the first Latino to hold the post if confirmed. Director of the National Institute of Allergy and Infectious Diseases Dr. Anthony Fauci, who is taking on the elevated role of chief medical adviser to Biden in the incoming administration, is expected to dial into Biden’s meeting, though not the one at the White House.

Biden and Vice President-elect Kamala Harris are also meeting Tuesday with several civil rights leaders including NAACP representatives to discuss policy issues around racial equity as well as diversity and representation on the incoming Cabinet. It comes after news leaked that Biden is expected to name retired four-star Army Gen. Lloyd Austin as his defense secretary, who would be the first African American in the post if confirmed, this week.

Tuesday is also the congressionally mandated "safe harbor" deadline -- the date, under federal law, by which the "final determination of any controversy or contest concerning the appointment" of electors "shall be conclusive” -- making it extremely difficult to dispute election results in the courts, where pro-Trump efforts have seen at least 39 defeats to date.