Passengers arrive for American Airlines flights at O’Hare International Airport in Chicago, Illinois on February 05, 2021.

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The US could still see a renewed spike in coronavirus – even if vaccinations against Covid-19 surge across the country – as states relax restrictions and more Americans travel to spring break, the centers’ head warned disease control and prevention on Monday.

“With warmer weather coming, I know it is tempting to relax and lose our vigilance, especially after a harsh winter that unfortunately saw the most cases and deaths during the pandemic,” said CDC Director Dr . Rochelle Walensky said at a press conference.

The Transportation Security Administration (TSA) examined more than 1.34 million people on Sunday, 86,000 more than the same day a year ago, shortly after the World Health Organization declared Covid-19 a pandemic.

TSA screenings have exceeded 1 million every day since Thursday. While air traffic is well below 2019 levels, despite the CDC’s warning of non-essential travel, more and more Americans are returning to heaven, even those who are fully vaccinated.

Although many colleges in the US have scaled back their spring break to curb parties and infection, Biden’s top government officials are still concerned about travelers “enjoying a maskless spring break,” Walensky said.

“I beg you, for the sake of the health of our nation,” Walensky said at the briefing on Monday. “The cases rose last spring, they rose again in the summer, they will climb now if we no longer take precautions, if more and more people are being vaccinated.”

Even with infections declining and vaccine adoption rapidly growing, the US continues to report a dangerously high baseline of daily cases that could be higher if Americans lose their vigilance, Biden’s top health officials have warned. Around 37.5 million people in the US, about 11% of the population, have been fully vaccinated to date, according to the CDC.

The U.S. has come a long way since early January when it hit a weekly average of just over 250,000 new cases per day. According to a CNBC analysis of data compiled by Johns Hopkins University, the nation reports an average of 53,670 new infections per day for the past week, a 10% decrease from the previous week.

– Leslie Josephs of CNBC and the Associated Press contributed to this report.