CNN  — 

President Joe Biden sharply criticized states such as Texas and Mississippi for lifting Covid-19 restrictions against pleas from the US Centers for Disease Control and Prevention and other top public health officials, accusing those in power of “Neanderthal thinking.”

“I think it’s a big mistake. Look, I hope everybody’s realized by now, these masks make a difference. We are on the cusp of being able to fundamentally change the nature of this disease because of the way in which we’re able to get vaccines in people’s arms,” Biden said when asked about the decisions by GOP Govs. Greg Abbott of Texas and Tate Reeves of Mississippi to relax restrictions.

“The last thing – the last thing we need is Neanderthal thinking that in the meantime, everything’s fine, take off your mask, forget it. It still matters,” Biden said, referencing a card he keeps in his pocket with the daily death toll of the virus amid his administration’s push to get vaccines into arms.

Biden, who is meeting with a bipartisan group of lawmakers in the Oval Office on the subject of ending cancer, called on all Americans to continue to follow guidelines despite the mixed messaging from some state officials.

“It’s critical – critical, critical, critical – that they follow the science: Wash your hands, hot water, do it frequently. Wear a mask and stay socially distanced. And I know you all know that. I wish the heck some of our elected officials knew it,” he told reporters.

Abbott and Reeves both announced this week that they were lifting mask mandates in Texas and Mississippi and will allow business to operate at full capacity. The decisions come as health experts caution that relaxing restrictions now could lead to another surge in coronavirus cases, especially as variants continue to spread.

Abbott’s press secretary, Renae Eze, told CNN in a statement that Abbott “was clear in telling Texans that COVID hasn’t ended, and that all Texans should follow medical advice and safe practices to continue containing COVID.”

“It is clear from the recoveries, the vaccinations, the reduced hospitalizations, and the safe practices that Texans are using, that state mandates are no longer needed. We must now do more to restore livelihoods and normalcy for Texans,” Eze’s statement said. “The Governor’s focus has been, and always will be, protecting the lives and livelihoods of Texans.”

Reeves took a shot at Biden’s age while defending his decision.

“Given how long ago Mr. Biden was elected to the US Congress, he certainly should know how Neanderthals think,” Reeves said. “But here’s the reality, I trust the people of Mississippi to make the right decisions. I trust the American people to make the right decisions. The fact of the matter is, you cannot focus on data and science and making good decisions on those days when the numbers are going up and ignore the data and science on those days when the numbers are going down. And the fact of the matter is that we’ve seen significant drops.”

Dr. Anthony Fauci, the nation’s top infectious disease expert and Biden’s chief medical adviser, criticized the states’ moves to lift restrictions, telling CNN’s Erin Burnett on “OutFront” on Wednesday that “it certainly, from a public health standpoint, is ill-advised.”

He pointed to previous attempts to reopen states that were followed by “rebounds” of the virus, calling it “inexplicable why you would want to pull back now” and reiterating that public health guidelines are “not arbitrary, they’re based on evidence and data from science.”

“Every single day that goes by, every week, we get more and more people vaccinated,” Fauci added. “So now is not the time to pull back. Now’s the time to really crush this by doing both public health measures and accelerating the vaccinations like we’re doing.”

After weeks of dropping case numbers, new infections are on the rise again – about 2% more this past week compared to the previous week, CDC Director Dr. Rochelle Walensky said Monday. More than 518,000 Americans have died from Covid-19, according to Johns Hopkins University.

“Please hear me clearly: At this level of cases with variants spreading we stand to completely lose the hard-earned ground we have gained. These variants are a very real threat to our people and our progress,” Walensky said Monday during a White House briefing.

Walensky added: “Now is not the time to relax the critical safeguards that we know can stop the spread of Covid-19 in our communities. Not when we are so close.”

Biden announced this week that the US would have enough Covid-19 vaccine doses for every adult American by the end of May, which is a two-month acceleration of the previous timeline his administration had laid out. But the President cautioned that the country must still take health and safety precautions and be vigilant against the virus.

Johnson & Johnson’s single-dose coronavirus vaccine, the third Covid-19 shot authorized for use in the US, has started to be administered this week.

On Wednesday, Walensky reiterated that she is encouraging individuals to wear masks and practice social distancing in order to protect their own health and stop the virus from spreading.

“Every individual is empowered to do the right thing here, regardless of what the states decide,” Walensky said.

This story has been updated with comments from Dr. Anthony Fauci.

CNN’s Caroline Kelly contributed to this report.