Former New Jersey Gov. Chris Christie spoke exclusively to ABC News on Friday morning for the first time since he tested positive for COVID-19 and was released from the hospital.

"It hits you like a freight train." Christie told ABC News chief anchor George Stephanopoulos in an interview on "Good Morning America." "It all happened very, very quickly. Within 24 hours, I went from feeling absolutely fine to being in the intensive care unit."

Christie, who has asthma, spent seven days in the ICU while battling COVID-19. He said he received an antibody treatment in combination with the antiviral medication remdesivir early on in the course of his illness.

"The last two or three days, I've really kind of turned around in terms of being able to recover and getting a lot of my energy back," he said. "So I'm not yet 100%, but I'm about a fighting 80%."

Christie admitted he "was wrong" and "made a mistake" in not wearing a face mask while recently helping President Donald Trump prepare for the debate.

"I was led to believe that all the people that I was interacting with at the White House had been tested and it gave you a false sense of security, and it was a mistake," he said. "I was doing it right for seven months and avoided the virus. I let my guard down for a couple days inside the White House grounds and it cost me unfortunately in a significant way."

Christie urged the public to wear masks, saying, "there is no downside to you wearing masks and, in fact, there can be a great deal of upside."

"I think no matter what you're doing, whether you're at a rally for your preferred candidate, whether you're out at the supermarket, whether you're at a protest, no matter what you're doing, you should have a mask on and you should try to remain socially distant from folks," he said. "I did it for seven months, George, and I stayed healthy. I didn't do it for four days and I wound up in the ICU."

Russia confirmed another 15,150 new cases of COVID-19 in the last 24 hours, its highest daily tally yet.

It's the first time since the start of the coronavirus pandemic that Russia has registered more than 15,000 cases in a single day. The latest daily case count is nearly 1,400 more than the previous day.

More than 33% of the newly confirmed cases were reported in the capital, Moscow, the epicenter of the country's COVID-19 outbreak, according to Russia's coronavirus response headquarters.

An additional 232 deaths from COVID-19 were also registered in the past 24 hours, down from the national record of 286 set the previous day. The cumulative totals now stand at 1,369,313 cases and 23,723 deaths, according to the country's coronavirus response headquarters.

Russia has been breaking its own records for daily case counts and deaths almost every day since Oct. 9. The country of 145 million people has the fourth-highest tally of COVID-19 cases in the world, behind only the United States, India and Brazil.

ABC News' Alina Lobzina contributed to this report.

Germany confirmed 7,334 new cases of COVID-19 on Thursday, its highest single-day increase since the start of the pandemic.

It's the first time Germany has surpassed 7,000 COVID-19 cases in a single day, and it marks the second straight day that the country has broken its own record for the daily tallies.

An additional 24 deaths from COVID-19 were also registered Thursday. The cumulative totals now stands at 348,557 cases and 9,734 deaths, according to the latest data from the country’s public health institute.

Until this week, Germany’s highest recorded figure was nearly 6,300 cases on March 28, according to data published by the Robert Koch Institute. While testing has increased since then, the country is among several in Europe that have seen a sharp uptick in COVID-19 infections in recent weeks.

Earlier this week, Germany's federal and state governments agreed to toughen rules on wearing face masks and to have bars close early in areas where infections are high.

There were 63,610 new cases of COVID-19 identified in the United States on Thursday, the country's highest daily tally since Aug. 14, according to a real-time count kept by Johns Hopkins University.

The latest daily tally is up by more than 4,000 from the previous day but still under the country’s record set on July 16, when there were 77,255 new cases in a 24-hour-reporting period.

An additional 904 coronavirus-related fatalities were also recorded Thursday, slightly less than the previous day and down from a peak of 2,666 new fatalities reported on April 17.

A total of 7,980,461 people in the United States have been diagnosed with COVID-19 since the pandemic began, and at least 217,700 of them have died, according to Johns Hopkins. The cases include people from all 50 U.S. states, Washington, D.C. and other U.S. territories as well as repatriated citizens.

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 and crossing 70,000 for the first time in mid-July. The daily tally of new cases has gradually come down since then but has started to climb again in recent weeks.

The number of new COVID-19 cases recorded in the United States continued to increase by double digits in week-over-week comparisons, while the number of new deaths from the disease continued to tick downward slightly, according to an internal memo from the U.S. Department of Health and Human Services that was obtained by ABC News on Wednesday night.