U.S. President Joe Biden's nominee to become surgeon general, Dr. Vivek Murthy, told The Washington Post Live that he thinks the United States has a "good shot" to get all kids in school by the fall.

Murthy, a physician who served as U.S. surgeon general from 2014 to 2017, said the nation must takes these steps: vaccinate staff; ensure schools have the resources to take precautionary measures including PPE and tests; and lower "background rates of infection," which he defines as rates of transmission in the community.

"When those rates are really high, it makes it harder to prevent infection from getting into the school," Murthy said. "So we've got to get that background infection rate down, and we've got to vaccinate teachers and other educators and staff in schools. As well as, when we do have the opportunity to vaccinate kids when the trial data comes through and shows that it is safe and effective, that we've got to start vaccinating children, too."

ABC News’ Anne Flaherty contributed to this report.

The United States’ first known cases of the South Africa variant of the novel coronavirus have been confirmed in two people in South Carolina, according to the South Carolina Department of Health and Environmental Control.

"There is no known travel history and no connection between these two cases," the department said in a statement Thursday.

Both cases are among adults, one who is from the Lowcountry region and another who is from the Pee Dee region, according to the department.

The U.S. Centers for Disease Control and Prevention said it's aware of the cases and it "recommends that people avoid travel at this time."

The so-called B1351 variant, first identified in South Africa, has been detected in more than 30 countries, according to the South Carolina Department of Health and Environmental Control.

"Experts agree that existing vaccines work to protect us from this variant, even if we don’t know precisely how effective they are," the department said. "At this time, there’s no evidence to suggest that the B.1.351 variant causes more severe illness."

During an interview Thursday on ABC's "Good Morning America," Dr. Anthony Fauci, chief medical adviser to U.S. President Joe Biden and the nation's leading infectious disease expert, said the South Africa variant "troubles" him.

Fauci said lab experiments show the neutralizing antibodies induced by existing COVID-19 vaccines are "diminished by multifold" when tested against the B1351 variant

"It's still within the range of what you would predict to be protective," he said, "but I take no great comfort in that."

However, scientists are already working on vaccines that will specifically target the South Africa variant, according to Fauci.

"May not be necessary," he said, "but if it is we'll already be on the road to be able to give people a boost that directs against the South African isolate."

In the span of two weeks, the United States' seven-day average of daily COVID-19 cases has declined by 34% -- the steepest non-holiday-related drop in cases the country has seen since the summer, according to ABC News’ analysis of data compiled by The COVID Tracking Project, a volunteer-run effort to track the U.S. outbreak.

California appears to have seen the most drastic drop of any U.S. state, as its seven-day average of daily cases has been nearly slashed in half over the last two weeks.

Despite continued positive signs in case and hospitalization trends, daily death numbers are still incredibly high.

Another 3,943 fatalities from COVID-19 were reported on Wednesday, according to data collected by Johns Hopkins University -- that is approximately one death recorded every 22 seconds.

ABC News’ Arielle Mitropoulos contributed to this report.

COVID-19 cases and deaths are surging across Africa as new, more contagious variants of the novel coronavirus spread to additional countries, the World Health Organization warned Thursday.

"The variant which was first detected in South Africa has spread quickly beyond Africa and so what’s keeping me awake at night right now is that it’s very likely circulating in a number of African countries," Dr. Matshidiso Moeti, the WHO's regional director for Africa, said in a statement.

Diagnosed COVID-19 infections increased by 50% in Africa between Dec. 29 and Jan. 25, when compared with the previous four weeks. Deaths from the disease rose two-fold in the same period, with over 15,000 concentrated in 10 mainly southern and northern African nations, according to the WHO.

Over the last week, more than 175,000 new cases and over 6,200 new deaths were reported across the continent. There was a small dip in cases in South Africa, but 22 countries continue to see their numbers surge, according to the WHO.

The B1351 variant, first identified in South Africa, is "predominant and powering record case numbers in South Africa and the sub-region," the WHO said. The strain has been detected in Botswana, Ghana, Kenya, the French Indian Ocean region of Mayotte, Zambia and at least 24 non-African nations, according to the WHO.

Meanwhile, another new, highly contagious variant called B117, which was initially detected in the United Kingdom, has been found in Gambia and Nigeria.

The WHO said it is working to track and tackle new strains of the deadly virus. The U.N. agency, along with the Africa Centers for Disease Control and Prevention, has helped set up a COVID-19 genomic sequencing laboratory network with labs in the Democratic Republic of the Congo, Gambia, Ghana, Kenya, Nigeria, Senegal, South Africa and Uganda.

"In addition to the new variants, COVID-19 fatigue, and the aftermath of year-end gatherings risk powering a perfect storm and driving up Africa’s second wave and overwhelming health facilities," Moeti said. "Africa is at a crossroads. We must stick to our guns and double down on the tactics we know work so well. That is mask wearing, handwashing and safe social distancing. Countless lives depend on it."

Dr. Anthony Fauci, the nation's leading infectious disease expert, opened up about his experience working with former U.S. President Donald Trump in an interview with The New York Times that was published Sunday.

When COVID-19 began to rapidly spread in the northeastern part of the country last year, particularly in New York City, Fauci said Trump had "almost a reflex response" to try to "minimize" the situation.

"I would try to express the gravity of the situation, and the response of the president was always leaning toward, 'Well, it's not that bad, right?' And I would say, 'Yes, it is that bad,'" Fauci, director of the National Institute of Allergy and Infectious Diseases, told the newspaper. "It was almost a reflex response, trying to coax you to minimize it. Not saying, 'I want you to minimize it,' but, 'Oh, really, was it that bad?'"

Fauci, who was a key member of the Trump administration's coronavirus task force, said another thing that made him "really concerned" was the former president taking input from non-experts on unproven methods to treat COVID-19, like hydroxychloroquine.

"It was clear that he was getting input from people who were calling him up, I don’t know who, people he knew from business, saying, 'Hey, I heard about this drug, isn't it great?' or, 'Boy, this convalescent plasma is really phenomenal,'" Fauci told the newspaper. "And I would try to, you know, calmly explain that you find out if something works by doing an appropriate clinical trial; you get the information, you give it a peer review. And he’d say, 'Oh, no, no, no, no, no, no, no, this stuff really works.'"

"He would take just as seriously their opinion -- based on no data, just anecdote -- that something might really be important," Fauci added. "That’s when my anxiety started to escalate."

When the leadership of the White House coronavirus task force changed hands last February, with U.S. Vice President Mike Pence coordinating the government's response and Trump at the podium taking questions from reporters during the press briefings, Fauci said it went from "the standard kind of scientifically based, public-health-based meetings" to "the anecdotally driven situations, the minimization, the president surrounding himself with people saying things that didn’t make any scientific sense."

"Then I started getting anxious that this was not going in the right direction," he told the newspaper. "We would say things like: 'This is an outbreak. Infectious diseases run their own course unless one does something to intervene.' And then he would get up and start talking about, 'It’s going to go away, it’s magical, it’s going to disappear.'"

That's when Fauci said it became clear to him that he needed to speak up, even if it meant contradicting the president.

"He would say something that clearly was not correct, and then a reporter would say, 'Well, let’s hear from Dr. Fauci.' I would have to get up and say, 'No, I’m sorry, I do not think that is the case,' he told the newspaper. "It isn’t like I took any pleasure in contradicting the president of the United States. I have a great deal of respect for the office. But I made a decision that I just had to. Otherwise I would be compromising my own integrity, and be giving a false message to the world. If I didn’t speak up, it would be almost tacit approval that what he was saying was OK."

This upset Trump's "inner circle," Fauci said.

"That’s when we started getting into things I felt were unfortunate and somewhat nefarious -- namely, allowing Peter Navarro to write an editorial in USA Today saying I’m wrong on most of the things I say," he told the newspaper. "Or to have the White House press office send out a detailed list of things I said that turned out to be not true -- all of which were nonsense because they were all true. The very press office that was making decisions as to whether I can go on a TV show or talk to you."

Fauci said there were a couple times where Trump even called him personally to say, "Hey, why aren’t you more positive? You’ve got to take a positive attitude. Why are you so negativistic? Be more positive."

Fauci said he and his family have received death threats, beginning last March, and that his wife once suggested he consider quitting.

"But I felt that if I stepped down, that would leave a void. Someone’s got to not be afraid to speak out the truth," he told the newspaper. "Even if I wasn’t very effective in changing everybody's minds, the idea that they knew that nonsense could not be spouted without my pushing back on it, I felt was important. I think in the big picture, I felt it would be better for the country and better for the cause for me to stay, as opposed to walk away."