Researchers at Ohio State University's Wexner Medical Center said Wednesday that they've have identified two new variants of the virus that causes COVID-19.

The first variant, which was found in just one person, contains a mutation that's similar to a mutation seen in the variants from the U.K. and South Africa, but it arose independently in the U.S., the researchers said. It is not known if it is more easily transmissible.

The second newly identified variant was found in about 20 patients in Columbus and also arose independently in the U.S., the researchers said. It does not contain any mutations in common with variants identified in the U.K. or South Africa, they said. Scientists said they found cases of this variant with increased frequency during late December, which could imply that it's more easily transmissible, but they emphasized that more studies are needed.

Peter Mohler, a co-author of the study and chief scientific officer at the Wexner Medical Center, said Wednesday, "we’re not ready to overreact," stressing, "this is very normal for a virus to mutate."

ABC News' Sony Salzman contributed to this report.

With 4,327 confirmed deaths on Tuesday -- the deadliest day of the pandemic so far -- Tuesday’s death toll equaled about one American dying every 20 seconds.

The national average of daily cases is also at a record high, with 246,000 new cases every day.

In the last week, 22 states and Washington, D.C., have reported a record seven-day average of daily cases.

Since the beginning of the pandemic, at least 22.8 million Americans have contracted COVID-19 -- meaning about one in every 14 Americans has tested positive.

California has the most hospitalizations of any state with more than 22,000 patients, followed by Texas, New York, Florida and Georgia.

Arizona, Alabama and Nevada currently hold the highest hospitalizations rates per million people in the country.

ABC News’ Arielle Mitropoulos contributed to this report.

New York City Mayor Bill de Blasio is calling for "an immediate travel ban from the United Kingdom to the United States."

New York state has 12 cases of the U.K. coronavirus variant, de Blasio said. One of the two cases confirmed in New York City was someone who traveled to the U.K., he said.

“Someone who was in the U.K. has brought the variant back here. We need that stopped. Flights from the United Kingdom should be canceled immediately by the federal government,” de Blasio said.

Beginning Jan. 26, those flying to the U.S. from foreign countries must take a COVID-19 test within three days before their flight, and airlines must confirm the negative test before they board, the Centers for Disease Control and Prevention announced Tuesday.

The U.K. variant appears to spread more easily but there’s no evidence that it is more deadly.

Meanwhile, as New York vaccinates more residents, the mayor said, “even with normal supplies that we expect to have delivered next week, we will run out of vaccine as some point next week unless we get a major new resupply because so many New Yorkers want the vaccine and we have the ability to give it to them.”

“We need the federal government, the state government and the manufactures to step up and get us more supply immediately,” he said.

ABC News’ Rachel Katz contributed to this report.

Vatican City, an independent enclave surrounded by Rome that serves as the headquarters of the Roman Catholic Church, launched a COVID-19 vaccination campaign on Wednesday, according to Vatican spokesman Matteo Bruni.

Citizens of the tiny city-state along with employees and pensioners will have the opportunity to receive the vaccine, as well as family members who are entitled to use of the Vatican health care system. Priority is being given to health care workers, public safety personnel, the elderly and individuals who are most frequently in contact with the public, Bruni said.

It's unclear which COVID-19 vaccine the Vatican is using and how many doses have been procured so far. The city-state has a population of only around 800 people but employs more than 4,000.

The vaccination campaign is voluntary, and people under the age of 18 are being excluded for the time being, according to Bruni.

Pope Francis, who turned 84 last month and had part of a lung removed when he was younger, has said he plans to be vaccinated against COVID-19 as soon as possible.

Since the start of the pandemic, Vatican City has reported at least 27 confirmed cases of COVID-19, according to a real-time count kept by Johns Hopkins University.

Prince William championed the effort of the NHS, the U.K.'s health agency, in delivering the COVID-19 vaccine in a video posted to Kensington Royal's Twitter account Saturday night.

The video included several health care professionals on a Zoom call, along with the Duke of Cambridge, talking about distributing and delivering the vaccine.

"This is because we have a world-leading NHS, this is because we have the right people, the right research and development here," William says in the video.

William also encourages people to get the vaccine when they are eligible, noting his "grandparents" -- Queen Elizabeth and Prince Philip -- got the vaccine already. The palace said last week that Elizabeth, 94, and Philip, 99, had gotten the vaccine.

"My grandparents have had the vaccine and I'm very proud of them for doing that," he says in the video. "So it's really important that everyone gets their vaccine."