Still, there is real-world evidence that mandates work.
Dr. Offit said Mississippi, which has one of the nation’s lowest coronavirus vaccination rates, has extraordinarily high rates of childhood immunization because its state law does not allow philosophical or religious exemptions.
When a measles outbreak erupted among Orthodox Jews in Brooklyn two years ago, officials tried education and outreach, but Mayor Bill de Blasio ultimately declared a public health emergency requiring people in the Williamsburg neighborhood to be vaccinated. A month later, an anti-vaccine rally drew hundreds of Orthodox Jews. The state later repealed its religious exemption.
But in an era when public health has become politicized and state legislatures around the country are moving to restrict emergency health powers, some experts worry that if Mr. Biden begins to push for mandates, it would provoke conservative state lawmakers to undo requirements even for basic childhood vaccinations.
“There’s concern if you cause a lot of controversy and you open that whole thing up, not only could the legislature go in and say, ‘You’re not going to include Covid,’ but they could also tinker with the idea that maybe all of these childhood vaccines are an overreach of government,” Dr. Plescia, of the state and territorial health officials group, said.
In some states, including Florida and Texas, requiring proof of Covid-19 vaccination is already against the law. “In Florida, your personal choice regarding vaccinations will be protected,” Gov. Ron DeSantis of Florida said in May, after signing legislation barring businesses and government entities from requiring proof of coronavirus vaccination.
On Tuesday, Mr. Biden made it clear that he was running out of patience with people who refuse to get a shot that could save their lives and protect others.
“The more we learn about this virus and the Delta variation, the more we have to be worried or concerned,” Mr. Biden said. “And only one thing we know for sure: If those other 100 million people got vaccinated, we’d be in a very different world.”