WASHINGTON - Dr. Anthony Fauci, the top U.S. infectious disease expert, sounded new alarms Sunday about the surge in coronavirus cases in the country, especially in regions where people have been resistant to getting vaccinated even as the delta variant spreads rapidly.

"We're going in the wrong direction," Fauci said on CNN's "State of the Union" show. "Fifty percent of the country is not vaccinated. That's a problem."

"We're putting ourselves in danger," said Fauci, the top medical adviser to President Joe Biden.

In the United States, hospitalizations and deaths are far below their peaks last winter. But the number of new infections has been rising sharply in parts of the country where skepticism about the need to get vaccinated, the safety of the vaccines and resistance to government suggestions to get inoculated remain a potent force.

More than 51,000 new infections were recorded in the U.S. on Saturday, a 172% increase over the last two weeks, and more than 250 deaths have been occurring daily in recent weeks.

As it stands, the government says more than 162 million Americans have been fully vaccinated, which corresponds to 49% of the country's population and nearly 60% of adults.

But polls have shown that as many as 80% of unvaccinated Americans say they definitely will not get inoculated or are unlikely to, no matter how many officials urge them to get the shots.

Many conservative politicians previously had adopted a more cautious approach toward vaccinations or said whether to get inoculated was a matter of personal choice. Now some are voicing their exasperation at those refusing to get vaccinated.

Republican Governor Kay Ivey of Alabama said last week of the unvaccinated, "These people are choosing a horrible lifestyle."

Another Republican governor, Asa Hutchinson of Arkansas, has long urged vaccinations in his southern state but it still has one of the lowest rates of inoculations. Two adolescents recently died of COVID-19 in his state. COVID-19 is the disease caused by the coronavirus.

"These are alarm bells," he told CNN. Nonetheless, he noted, "Certainly the resistance (to inoculations) has hardened."

Arkansas Governor Asa Hutchinson shows a chart on vaccination rates at a town hall meeting in Batesville, July 12, 2021.

But Hutchinson voiced optimism that the unvaccinated will change their minds.

"People can change their resistance," he said. "That should be our focus."

Fauci said those vaccinated "are highly protected," including against the delta variant. But the pace of vaccinations has dropped in the U.S. by more than 80% since mid-April.

Some cities, including Los Angeles in the West and St. Louis in the middle of the country, have imposed new orders for people to wear masks in public indoor spaces regardless of vaccination status. Other cities are considering similar directives.