Gov. Pete Ricketts of Nebraska, also a Republican, similarly prohibited mask mandates in state office buildings.
“If somebody wants to wear a mask, that is their personal choice,” he said.
As political leaders embrace policies aimed at returning to normalcy, the vaccines are accentuating a chasm between the United States — where the shots are widely available and where doses are being offered to children — and other nations, such as Brazil and India, where the virus is still raging and vaccines are in short supply.
There are also reminders around the United States that the pandemic, and the partisan positioning around the crisis, remain far from over. The pace of vaccinations has declined sharply since mid-April, with providers administering about 1.7 million doses per day on average, about a 50 percent decrease from the peak of 3.38 million reported on April 13. As the Biden administration has shifted its vaccine strategy to more local and personalized efforts, states are trying different tactics, including offering $1 million vaccine lottery prizes and other incentives.
Gov. Andrew M. Cuomo of New York ordered flags to be flown at half-staff in remembrance of the frontline workers who died during the pandemic, only to have a top Republican leader in the State Senate demand an apology from the governor for such a move during a holiday honoring soldiers.
A year ago, President Donald J. Trump mocked Mr. Biden for appearing in public with a face mask. Some states that moved early to reopen, such as Arizona, Florida and Texas, were slammed with a surge in cases weeks later.
Dr. Diekema, the Iowa epidemiologist, said he hoped that the resurgence of the virus last summer would serve as a reminder of the risks to unvaccinated people.
He said he couldn’t imagine a year ago that more than half a million people in the United States would die because of the virus. And the toll continues to grow: Over the holiday weekend, Dr. Diekema said that he planned to be working.
“I’ll be in the hospital seeing patients with infectious diseases like Covid-19,” he said.