(CNN) -- The US just hit a record high of about 4.6 million doses of COVID-19 vaccines reported administered in one day, according to data published Saturday by the Centers for Disease Control and Prevention.
"Amazing Saturday! +4.63M doses administered over total yesterday, a new record," Dr. Cyrus Shahpar, the COVID-19 data director at the White House, wrote on Twitter. "More than 500K higher than old record last Saturday. Incredible number of doses administered."
The new record is great news -- but it comes at a complicated time in the pandemic for the US.
While COVID-19 vaccination numbers climb across the country, COVID-19 cases and hospitalizations are also on the rise, fueled by the B.1.1.7 variant, which is now the dominant strain in the US. Experts say the variant is more contagious, may cause more severe disease and is also potentially more deadly.
In the past seven days, the US has reported an average of more than 68,000 new COVID-19 cases daily, according to data from Johns Hopkins University. That's up by more than 20% since the March 10 seven-day average.
"On the one hand, we have so much reason for optimism and hope, and more Americans are being vaccinated," CDC Director Dr. Rochelle Walensky said during a White House COVID-19 briefing Friday. "On the other hand, cases and emergency room visits are up. And ... we are seeing these increases in younger adults, most of whom have not yet been vaccinated."
Americans ages 18 to 64 have seen increasing numbers of emergency department visits, she added.
And the trends are "magnified" in one part of the country, she said: the Upper Midwest.
"CDC is working closely with public health officials in this region to understand what is driving these cases and how we can intervene."
'A life and death race'
Michigan is currently among the hardest-hit states in the country and local officials say the state is in the middle of another surge, reporting thousands of new cases daily.
The state also has the second-highest number of reported cases of the B.1.1.7 variant after Florida, according to CDC data. And one expert says it's a combination of two factors that have driven up numbers.
"This B.1.1.7 variant... is more contagious and I think there's just fatigue from this pandemic out there so a lot of people don't wear masks, don't social distance, so we've basically taken a step back in Michigan," Dr. Paul Offit, director of the Vaccine Education Center at the Children's Hospital of Philadelphia, told CNN on Saturday.
"It's really frustrating, because we're almost there," he said. "We have to hang in there for the next two months and we're not doing that."
Amid the spiking numbers, some Michigan hospitals are delaying and rescheduling non-emergency procedures on a "case-by-case basis," a spokesperson for the Michigan Health & Hospital Association said.
"Hospitals want everyone to get the care they need and only reschedule procedures as a last resort," John Karasinski said Saturday. "We want to stress that hospitals are safe for all who need care and any individual with an emergency medical need should seek care immediately."
It's not just Michigan reporting alarming trends.
In both Michigan and Minnesota, "there is concern about transmission in youth sports -- both club sports, as well as sports affiliated in schools," Walensky said Friday.
Minnesota health officials warned Friday the state was seeing a "sharp increase" in COVID-19 cases, adding it is "more important than ever" to keep practicing safety measures like wearing a mask and social distancing.
In Ohio, Gov. Mike DeWine said Thursday the number of COVID-19 cases, hospitalizations and ICU admissions are all rising.
"We're moving now in the wrong direction," he said. "More than half of our counties, 53, have seen increases."
"We can still turn this around if more people continue to get vaccinated," the governor added. "This is a race. We are in a race. And it's a life and death race."
Health official: Do these two things
So far, 35.3% of the American population has gotten at least one dose of a COVID-19 vaccine, CDC data shows. And about 21.3% has been fully vaccinated.
That means tens of millions of Americans are still not vaccinated and remain vulnerable to the virus.
So as the country works to boost vaccination numbers and reach the levels needed to control the spread, experts say Americans should stay vigilant and continue taking precautions.
"To end this pandemic, this is what we have to do," US Surgeon General Dr. Vivek Murthy said Friday in the White House briefing. "We've got to step up and help protect one another. And that's why today I'm asking everyone to do two things: One, get vaccinated as soon as you can. And two, help the people you care about get vaccinated as well."
In an interview published last week, Dr. Anthony Fauci told Business Insider that even though he is fully vaccinated against COVID-19, he still won't go to a restaurant or a movie theater.
"I don't think I would -- even if I'm vaccinated -- go into an indoor, crowded place where people are not wearing masks," Fauci said.
CNN's Amanda Sealy, Sarah Boxer, Ben Tinker, Polo Sandoval and Pamela Brown contributed to this report.