(CNN) The number of new Covid-19 cases has plateaued at a "disturbingly high level," and the US is at risk from a new surge, Dr. Anthony Fauci warned on Wednesday.
While lower than the peak earlier this year, there were still more than 61,000 new cases reported on Wednesday, according to data from Johns Hopkins University. And the lack of continued significant decreases in infections is a concern, the director of the National Institute of Allergy and Infectious Diseases told CNN's Anderson Cooper, particularly given the spread of variants.
"It's almost a race between getting people vaccinated and this surge that seems to want to increase," Fauci said, noting Europe is experiencing a spike much like the one experts worry about for the US.
The US is vaccinating people quickly, with more than 33% of the population -- more than 112 million people -- having received at least one dose of a vaccine, according to data from the Centers for Disease Control and Prevention. About a quarter of US adults -- more than 66 million people -- are fully vaccinated.
Those vaccines may be behind the decrease in Covid-19 fatalities, CDC Director Dr. Rochelle Walensky said Wednesday.
But the pace of getting vaccines into the arms of Americans will need to keep increasing now that the virus variant first identified in the United Kingdom, known to be more transmissible and believed to be more deadly, is the most common strain in the US, Walensky said.
To fight the variant, Fauci urged Americans to get vaccinated and stick to preventative measures.
"Hang in there a bit longer," he said. "Now is not the time, as I've said so many times, to declare victory prematurely."
The country's daily rate of new coronavirus cases rose over most of the last four weeks. Part of that is due to the spread of B.1.1.7 and other concerning variants, Walensky said earlier this week.
The US has averaged more than 64,760 new coronavirus cases a day over the past week -- slightly lower than week prior, but still about 21% higher than two weeks ago, and more than 12% higher than four weeks ago, according to Johns Hopkins.
While many states have seen new cases decreasing, several have witnessed large increases, including North Dakota, Montana and Michigan. Each has seen an increase of more than 50% in new cases in the last 30 days compared to the 30 days prior, according to a CNN analysis of Johns Hopkins data.
Recent infections have skewed toward younger people, which Fauci said can be attributed in part to so many older people being vaccinated. More than 75% of people ages 65 years and older have received at least one shot of the Covid-19 vaccine in the US, he noted.
Dr. Leana Wen, a CNN medical analyst and former Baltimore health commissioner, agreed. She believes the country is in the middle of a fourth surge. But this surge looks different than its predecessors because many of the people most vulnerable to the coronavirus are vaccinated, she said.
"Before we would have seen a steeper rise in the number of cases followed by a steep rise in hospitalizations and deaths," she told CNN. "This time, that's blunted a lot because the most vulnerable are vaccinated."
"But at the same time," she said, "we are seeing a higher proportion of younger people who are getting ill and unfortunately getting hospitalized."
As the cases trend toward younger Americans, many schools are expanding access to full in-person learning. About three-quarters of US public schools are open for full time in-person or hybrid learning.
Still, many remain in remote learning. Just 39% of 4th graders and 29% of 8th graders, for example, were attending full time, in-person school, according to data released Wednesday by the Department of Education's National Assessment of Educational Progress.
The data stems from a nationwide survey of school districts looking at 4th and 8th grades, assessing the methods of instruction available along with what proportion of students are using those methods.
Additionally, the data break down students attending in-person learning, with more than half of Black, Hispanic and Asian 4th graders learning remotely, while nearly half of White 4th graders learning in-person.
Those students returning to school are not yet eligible for vaccines, though studies will hopefully show the effectiveness of vaccinations in children as young as six months in the coming months, Fauci said.
Until then, students under 16 should continue wearing masks, avoiding close contact and avoiding indoor settings, Fauci said.
On Thursday, officials announced changes to the rules dictating closures in New York City schools, where at least some students at all grade levels have been welcomed back for in-person learning.
For individual classrooms, one confirmed case would require remote learning, Mayor Bill de Blasio said, and after 10 days the classroom would come back to in person learning. For an entire school, two cases, or three cases in a week, would lead to an increase in testing but would not be enough to close the school, he said.
Schools will only close when there are four or more cases in different classrooms that can be traced to a known exposure within the school, he said. In those cases, a school will close for 10 days.
New York City Health Commissioner David Chokshi said that the city will "continue to have the most rigorous measures of any public school system in the nation," adding that classroom and school closure rules "will remain stricter than the CDC's recommendation."
As the US races to vaccinate people, experts and officials are contending with adverse reactions believed to be linked to some shots.
Operations were paused at Dick's Sporting Goods Park in Colorado on Wednesday after health officials reported that 11 people who received their vaccinations became ill.
Those patients experienced symptoms like nausea and dizziness and were transported to a local hospital for observation out of an abundance of caution, according to a news release from the Colorado State Joint Information Center.
Although the cases might sound concerning, state officials said they don't have reason to believe that people vaccinated at the center should be concerned.
"The state has no reason to believe that people who were vaccinated today at Dick's Sporting Goods Park should be concerned," state officials said.
"From what we know, today's side effects were consistent with what can be expected," said Scott Bookman, COVID-19 Incident Commander in the news release. "Getting a vaccine is far safer than getting severely sick with COVID-19."