Even as President Biden on Thursday announced a more ambitious target of vaccinating 200 million Americans during his early months in office, the United States is once again experiencing a surge in Covid-19 cases, leading experts to warn the country has not yet defeated the novel coronavirus.

America's vaccination campaign accelerates

The United States last week administered an average of 2.5 million Covid-19 vaccine doses per day—up from an average of 2 million vaccine doses per day at the beginning of March, according to Bloomberg's Vaccine Tracker.

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If the United States continues to administer vaccine does at this pace, the country would surpass President Biden's new goal of administering 200 million doses before his 100th day in office—an increase from the 100 million dose target that Biden had announced at the time of his inauguration.

Biden announced the updated goal during a news conference Thursday, the New York Times reports. 

According to CDC data, about 133.3 million doses of the vaccines had been administered in the United states as of Thursday morning. About 87.3 million Americans had received at least one dose, and about 47.4 million had been fully vaccinated, the data shows.

Overall, 26% of the U.S. population has received at least one dose of a Covid-19 vaccine, and 14.3% have been fully vaccinated as of Thursday morning, the data shows. When broken down by age groups, the data shows 71% of Americans ages 65 and older—who are among the most vulnerable to severe cases of Covid-19—have received at least one dose of a Coivd-19 vaccine, and more than 44% have been fully vaccinated against the coronavirus.

Coronavirus cases rise amid America's vaccine rollout

Although vaccinations have accelerated, recent data indicates the number of coronavirus cases is climbing once again after declining for months. 

According to data compiled by the Times, the United States' average daily number of newly reported coronavirus cases over the past week was 58,579—up by 3% compared with the average from two weeks ago.

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The Times' data showed that, as of Friday morning, the rates of newly reported coronavirus cases were "staying high" in 25 states that have reported a daily average of at least 15 newly reported cases per 100,000 people over the past week. Those states are Alaska, Colorado, Connecticut, Delaware, Florida, Idaho, Illinois, Iowa, Maryland, Massachusetts, Michigan, Minnesota, Montana, New Hampshire, New Jersey, New York, North Carolina, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Vermont, Virginia, and West Virginia.

In addition, the rate of newly reported coronavirus cases was "going up" as of Friday morning in Hawaii, Oregon, Washington, and the U.S. Virgin Islands, which have had comparatively lower case rates, the Times reports.

Even as cases are increasing, new hospitalizations and deaths are continuing to decline. According to the Times' data, 39,439 Americans with Covid-19 were hospitalized on Thursday—down by 10% from the average from two weeks ago. Further, 1,270 new deaths were linked to the coronavirus on Thursday, down 31% from the average two weeks ago.

Two key reasons why cases are rising

Ali Mokdad, a professor of health metrics sciences at the University of Washington's Institute for Health Metrics and Evaluation (IHME), said the latest data indicates the United States is experiencing "a localized surge" in coronavirus cases, "but we could see it everywhere … [i]f we are not quick to dialing back or imposing mandates to slow down the surge." Mokdad added, "We are not out of danger."

Experts have said the recent uptick in coronavirus cases likely stems from two key factors: states easing coronavirus-related restrictions, and the spread of more transmissible coronavirus variants.

CDC Director Rochelle Walensky said she's concerned eased restrictions coupled with spring break could hurt the progress the United States has made in containing the coronavirus epidemic.

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"What concerns me is the footage of what's happening in spring breakers, in people who are not continuing to implement prevention strategies while we get fully scaled up," Walensky said during a White House Covid-19 briefing. "We need to hang in there for just a little while longer because we can see a time in the next couple of months where we will have a lot more people vaccinated and we will really be able to blunt infection rates," she added.

Meanwhile, IHME attributed the increase in cases in the northern half of the United States in part to "the spread of the B.1.1.7 variant." CDC is currently studying the spread of more contagious variants in the United States, Roll Call reports.

Health officials are urging states to not ease measures aimed at containing the coronavirus until a larger share of the U.S. population is vaccinated—and they're asking Americans to continue to wear face masks and follow other precautions.

"I'm often asked, 'Are we turning the corner?' My response is really more like, 'We are at the corner. Whether or not we turn the corner remains to be seen,'" Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and chief medical advisor for the White House's Covid-19 response, said at a press briefing. "We do have a lot of challenges in front of us with regard to the high level of daily infections" (Stolberg, New York Times, 3/25; Watson/Johnson, Associated Press, 3/26; Gorman, Reuters, 3/25; Querolo/Court, Bloomberg, 3/25; Sullivan, The Hill, 3/24; Baker/Witherspoon, Axios, 3/25; Caldwell, CNN, 3/26; Kopp, Roll Call, 3/24; Maxouris/Colbert, CNN, 3/26;