The possibility of obtaining herd immunity by the time summer is over and a new school year begins may be an "ambitious goal," Vivek Murthy, President Joe Biden's nominee for U.S. surgeon general, told George Stephanopoulos on "This Week" Sunday.

"I think what -- I think we can see improvement," Murthy said. "I think we can see reductions in cases and hospitalizations and deaths. I think we can see many more people immunized."

The "important thing" will be getting as many people vaccinated as possible, Murthy added.

"The more people we vaccinate, the better we will do, the fewer outbreaks we will see, the sooner we can get back to our way of life," he said.

Murthy also emphasized the importance of dispelling misinformation as well as continuing to take the necessary precautions, such as wearing masks and avoiding indoor gatherings.

"Then I think we can be on a path to not only turning the pandemic around, but, most importantly, getting our schools open, our workplaces back up and running, and regaining our way of life," he said.

The U.S. has surpassed 25 million cases of COVID-19, according to a Johns Hopkins University tally.

The national total confirmed case count currently sits at 25,003,695.

Last week, the U.S. surpassed 400,000 deaths from the virus. The death toll is currently at 417,463 in the U.S. and at 2,122,766 worldwide.

The number of global confirmed cases is nearing 100 million, currently sitting at 98,853,428.

-ABC News’ Joshua Hoyos

There have now been more than 20 million vaccine doses given out in the U.S., the CDC reported on Saturday.

The milestone was reached 23 days after the goal set by former President Donald Trump administration's Operation Warp Speed to reach that number of doses by the end of 2020.

President Joe Biden's administration has pledged to distribute 100 million doses in the first 100 days, as well as ramp up production of materials to administer vaccines amid an increase in demand and shortages of supply at the state level.

-ABC News' Ahmad Hemingway contributed to this report.

The University of Michigan has paused all athletics, including men's and women's basketball, for at least 14 days following "several" positive tests by people within the Michigan Athletic Department. The positive tests were also for the so-called U.K. variant, a more-contagious version of the virus. The decision to pause athletics was made in part due to the fact the tests were for the B.1.1.7 variant.

The decision was made not by the school but by the Michigan Department of Health and Human Services. The athletic programs will not be able to play or practice during the period.

"Canceling competitions is never something we want to do, but with so many unknowns about this variant of COVID-19, we must do everything we can to minimize the spread among student-athletes, coaches, staff, and to the student-athletes at other schools," Athletic Director Warde Manuel said in a statement.

The Wolverines men's basketball team, which is currently ranked No. 7 in the latest Associated Press poll, last played Friday against Purdue. Michigan won, 70-53, to advance to 13-1. They currently lead the Big Ten Conference at 8-1. They were supposed to play on Wednesday at Penn State.

The women's basketball team, currently 10-1 overall and ranked No. 11, was supposed to play Purdue on Sunday. The powerhouse men's ice hockey program, ranked in the top 10 nationally, will be affected as well.

The school said no determination has been made on how games scheduled to be played through Feb. 7 will be impacted.

Wednesday marks one year since the Centers for Disease Control and Prevention confirmed the first case of COVID-19 in the United States.

It wouldn't be until several months later that scientists identified the virus that caused COVID-19 in blood samples from people in various U.S. states as early as December 2019.

Since the first confirmed case 365 days ago, more than 24.2 million people in the U.S. have tested positive for COVID-19, which means that approximately one in every 13 Americans have contracted the disease, according to data collected by Johns Hopkins University.

At least 402,400 lives in the U.S. have been lost to COVID-19, representing approximately 19.5% of the worldwide death toll from the disease. That means one in every 823 Americans have now died from COVID-19.

New York remains the worst-hit U.S. state in terms of COVID-19 deaths -- with more than 37,000 confirmed fatalities -- followed by Texas, California and Florida.

Since the start of the pandemic, nearly 763,000 people in the U.S. have been hospitalized with COVID-19. Just under 124,000 people nationwide are currently hospitalized with the disease. In the last two weeks, that number has declined by 5.6%, according to data compiled by The COVID Tracking Project, a volunteer-run effort to track the U.S. outbreak.

January has already proven to be one of the worst months on record for the U.S. outbreak. In the first 19 days of 2021, the country has confirmed more than 4.15 million cases and over 55,000 deaths from the disease.

Although the numbers are currently impacted by the holiday weekend, the U.S. continues to see a drop in new infections, now averaging approximately 197,000 newly confirmed cases per day, according to The COVID Tracking Project.

ABC News' Brian Hartman and Arielle Mitropoulos contributed to this report.