There were 142,511 new cases of COVID-19 confirmed in the United States on Tuesday, according to a real-time count kept by Johns Hopkins University.

Tuesday's case count is far less than the country's all-time high of 298,031 newly confirmed infections on Jan. 2, Johns Hopkins data shows.

An additional 3,990 fatalities from COVID-19 were registered nationwide on Tuesday, down from a peak of 4,462 new deaths on Jan. 12, according to Johns Hopkins data.

COVID-19 data may be skewed due to possible lags in reporting over the Martin Luther King Jr. Day holiday weekend.

A total of 25,443,700 people in the U.S. have been diagnosed with COVID-19 since the pandemic began, and at least 425,216 have died, according to Johns Hopkins data. The cases include people from all 50 U.S. states, Washington, D.C., and other U.S. territories as well as repatriated citizens.

Much of the country was under lockdown by the end of March as the first wave of pandemic hit. By May 20, all U.S. states had begun lifting stay-at-home orders and other restrictions put in place to curb the spread of the novel coronavirus. The day-to-day increase in the country's cases then hovered around 20,000 for a couple of weeks before shooting back up over the summer.

The numbers lingered around 40,000 to 50,000 from mid-August through early October before surging again to record levels, crossing 100,000 for the first time on Nov. 4, then reaching 200,000 on Nov. 27 before nearing 300,000 on Jan. 2.

So far, the U.S. Food and Drug Administration has authorized two COVID-19 vaccines for emergency use -- one developed by U.S. pharmaceutical giant Pfizer and its German partner BioNTech, and another developed by American biotechnology company Moderna and the National Institute of Allergy and Infectious Diseases.

COVID-19 hospitalizations in the United States continue to trend downward, but the country's daily death rate is still above 3,000, according to The COVID Tracking Project, a volunteer-run effort to track the U.S. outbreak.

There are 108,957 people currently hospitalized with COVID-19 in the U.S., which is almost 30,000 fewer cases than a couple of weeks ago, the group said.

The country's seven-day average of daily COVID-19 deaths is now at 3,302, according to The COVID Tracking Project.

"While cases and hospitalizations are falling, the 7-day average for deaths jumped up today. That's because last Tuesday's data was depressed by the holiday," the group wrote on Twitter Tuesday. "We do expect, however, that deaths could stay elevated for quite a while."

U.S. President Joe Biden's administration said it has secured commitments from manufacturers to buy another 200 million doses of COVID-19 vaccines to arrive this summer -- 100 million from Pfizer and 100 million from Moderna.

This raises the total to 600 million and ensures the U.S. will eventually have two shots for nearly every American.

"We expect these vaccines to be available in production over the course of the summer," a Biden official said Tuesday.

Buying more doses had always been an option for the U.S. government as part of the prior contracts.

"We will increase overall weekly vaccination distributions of states, tribes and territories from 8.6 million doses to a minimum of 10 million doses starting next week," Biden said Tuesday.

The president also vowed to increase "transparency with states, cities and tribes and local partners when it comes to the vaccine supply."

"From this week forward," he said, "states, tribes and territories will now always have a reliable, three-week forecast with the supply they're going to get."

ABC News’ Anne Flaherty contributed to this report.

U.S. Vice President Kamala Harris, while wearing two face masks, received her second COVID-19 vaccine dose on Tuesday at the National Institutes of Health in Bethesda, Maryland.

Harris described the shot as "relatively painless," adding, "We’re going to get 100 million vaccinations in 100 days."

"I want to urge everyone to take the vaccine when it is your turn," she said.

Harris' husband, second gentleman Doug Emhoff, also received his second vaccine dose Tuesday.

Dr. Anthony Fauci, chief medical adviser to U.S. President Joe Biden and the nation's leading infectious disease expert, said Americans can expect to see more COVID-19 vaccine doses available throughout the country in the coming weeks.

"As we get into February, March and April, we're going to see an escalation of availability of doses that we may have not had a week or two or three ago," Fauci, who is also the director of the National Institute of Allergy and Infectious Diseases, told ABC News chief anchor George Stephanopoulos Thursday on "Good Morning America."

Although COVID-19 data is starting to show some promising trends, Fauci said the U.S. outbreak is "still a very serious situation."

"If you look throughout the country, the dynamics of the outbreak are a little bit unstable," he noted, "even though for the most part we're seeing general trends, seven-day trends of cases going down and ultimately, hopefully, hospitalizations and deaths."

When asked about reopening schools safely, Fauci said COVID-19 transmission rates in schools actually appear to be less than in communities when the schools have the resources and protection they need.

"So if you have a situation where you have dynamics of a viral spread in a community, it's less likely that the children who are in the school -- if we do things right, it's less likely that they're going to get infected," he said. "Obviously we want to get the teachers vaccinated, we want to make sure they have the resources to do it correctly. But when you look at the history of how this virus is moving in schools, it seems to be less spreading there than it is in the community."

Fauci also expressed concern over the new, more contagious variant of the novel coronavirus that was first identified in South Africa and has since spread to dozens of other nations, including the United States.

"The one in South Africa, George, troubles me," he said, explaining that lab experiments show the neutralizing antibodies induced by existing COVID-19 vaccines are "diminished by multifold" when tested against the South Africa variant, called B1351.

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

However, scientists are already working on vaccines that will specifically target the South Africa strain, 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."