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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."

Two pieces of economic data released Thursday highlight the pain of the U.S. economy as the coronavirus pandemic rages on.

Some 847,000 people nationwide lost their jobs and filed for unemployment insurance last week, according to the U.S. Department of Labor. That's a decrease of 67,000 compared to the previous week’s figure.

In addition, the Department of Labor said more than 18 million people were still claiming some form of unemployment benefits through all U.S. government programs as of the week ending Jan. 9. For the comparable week last year, that number was approximately 2 million.

While the weekly unemployment filings figure has dropped off significantly since peaking at some 6.9 million in a single week last spring, they still remain at historically high levels.

Meanwhile, the U.S. Department of Commerce said Thursday that U.S. gross domestic product grew at a 4% annualized rate last quarter -- a significant slowdown compared to the previous quarter, which saw an increase of 33.4% on an annualized basis. The third quarter’s huge spike, however, reflected businesses reopening after mass shutdowns.

ABC News’ Catherine Thorbecke contributed to this report.