The CDC is tracking a recent uptick in Covid-19 cases. Its chief says spring breakers and eased restrictions concern her

Top US health officials say they’re encouraged by the accelerating Covid-19 vaccinations.

But not enough Americans are fully vaccinated yet to suppress the spread of the virus – and eased restrictions across the country coupled with spring break crowds could spell trouble, one expert said Wednesday.

“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,” US Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said during a White House Covid-19 briefing.

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“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.

The coming weeks are especially critical: Covid-19 cases in the country have seen a slight increase, according to Walensky, while a highly contagious – and potentially more deadly – variant is circulating. Some experts have warned that by getting lax with safety measures, the country could see infections surge again.

“If we choose to invest in prevention right now, we will ultimately come out of this pandemic faster and with fewer lives lost,” the CDC director said.

So while the US is getting closer to turning the corner, it’s not there yet. The country continues to add tens of thousands of new cases and hundreds of virus-related deaths every day.

“When you are at that level, I don’t think you can declare victory and say you’ve turned the corner,” Dr. Anthony Fauci, the nation’s leading infectious disease expert, said during the briefing. “You’ve got to continue to do what we’re doing: more vaccinations and continue to do public health measures until we actually do turn the corner.”

You asked, we answered: Your top questions about Covid-19 and vaccines

People relax on the beach in Miami Beach, Florida, on March 23, 2021

‘A jolt of hope for all of us’

The good news: Vaccinations are already making a difference.

More than a quarter of Americans have gotten at least one dose of a Covid-19 vaccine, according to CDC data. About 14% of the US population is fully vaccinated.

The pace of vaccinations has doubled in less than two months, the CDC data shows, and now more than 70% of people 65 and older have received at least one shot.

A healthcare worker administers the Pfizer-BioNtech Covid-19 vaccine to residents and staff members at a retirement community in Pompano Beach, Florida, on January 6.

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That 65 and older population has also seen a larger decline in Covid-19 case rates, death rates and hospitalizations than any other age group and now account for a smaller share of total hospitalizations than they did a few months ago, according to an analysis of CDC data.

Track Covid-19 vaccinations in the US

In nursing homes, which were prioritized for vaccinations nationwide since the start of the rollouts, Covid-19 cases and deaths among residents are the lowest they’ve been since tracking began back in May, according to data from the Centers for Medicare & Medicaid Services.

Several recent studies also showed vaccines protected health care workers, Walensky and Fauci said during the Wednesday briefing.

“These findings should be a jolt of hope for all of us and to serve as a catalyst for everyone to roll up their sleeves when the vaccine is available,” Walensky said.

In total, vaccines have likely already saved at least 40,000 American lives so far, former CDC Director Dr. Tom Frieden told CNN on Wednesday night. “They’re remarkably effective, they’re remarkably safe,” Frieden said.

More states are expanding vaccine eligibility

As more states try to get more shots into arms faster, officials have unveiled timelines for expanded eligibility – and in many cases have set a date for when the vaccines will be open to anyone 16 and older.

Pfizer’s vaccine is the only one available for use by people who are 16 and older, while the Moderna and Johnson & Johnson vaccines are both authorized for people 18 and older.

Vaccine eligibility across the country

North Carolina and California are the latest states to expand vaccine eligibility.

All Californians over the age of 16 can get vaccinated starting April 15, Gov. Gavin Newsom announced Thursday. Those aged 50 and older can get vaccinated starting April 1.

California currently receives about 1.8 million doses of the vaccine per week, according to a press release from the governor’s office.

But based on the current estimates, the state said it expects to allocate “approximately 2.5 million first and second doses per week in the first half of April, and more than 3 million doses in the second half of April.”

North Carolina Gov. Roy Cooper announced that the state will be expanding vaccine eligibility to all adults starting April 7.

“I’m encouraged that North Carolina will be able to open eligibility to all adults well ahead of the president’s May 1st goal,” Cooper said in a press conference Thursday afternoon.

Earlier Thursday, Florida Gov. Ron DeSantis announced that vaccinations in his state will be open to anyone over the age of 18 beginning April 5. Starting Monday, March 29, Floridians 40 and over can get vaccinated.

What could stand in the way of more vaccinations

As vaccine eligibility opens up, some local officials worry that soon the challenge will be short demand, rather than short supply.

This picture shows vials of the AstraZeneca Covid-19 vaccine at a pharmacy in Paris on February 25, 2021. - Private practitioners in France started vaccinating vulnerable patients between 50 and 64 at their medical offices on February 25, as part of a new stage in the country's Covid-19 vaccination campaign.

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That could happen within the next four to six weeks, says Lori Tremmel Freeman, CEO of the National Association of County and City Health Officials.

“We will get to the point pretty quickly where we’re saying, ‘OK, now we’re into the really hard phase of this where we’re down to the population that is not so willing to get the vaccine,’” Freeman said.

It’s that last mile of “people that are hesitant” that will be challenging, she added. And other experts and officials have also expressed concern about that last stretch.

“The hesitancy is worrisome not just here, but all across the country, and I expect as a country we’ll get to 50% vaccination rate of the population. But we’re going to have a harder time getting from 50% to 70%,” Arkansas Gov. Asa Hutchinson told CNN earlier this week.

“It’s about overcoming the skepticism, it is about education,” he said.

Pfizer begins vaccine trial in children ages 5 to 11

Researchers at Duke University have begun testing Pfizer’s coronavirus vaccine in children under the age of 12, the company told CNN on Thursday. At least two children have already received the first shot.

The company is beginning the trials first in the 5- to 11-year-old age group to determine the appropriate dosage

The trial will enroll 144 children below the age of 12. Two thirds of the children will receive vaccine and one third will receive placebo. At a six-month follow up, all participants will be unblinded, and those on placebo will be eligible for the vaccine.

Pfizer has already evaluated the vaccine in 2,259 children between the ages of 12 and 15. The company told CNN that the tolerability findings were strong enough among this age group to encourage trials in younger children. It anticipates being able to share the data about the safety and efficacy of the vaccine in the older age group soon.

Results from the under-12 trial are expected by the end of 2021.

The Pfizer vaccine currently has an emergency authorization from the US Food and Drug Administration for those 16 and older.

CNN’s Deidre McPhillips, Jacqueline Howard, Deanna Hackney, Nadia Kounang,Chris Boyette, and Amanda Sealy contributed to this report.