Dr. Carroll is the chief health officer for Indiana University. He’s also a writer who focuses on health research and policy.

It would be nice if the United States could reach herd immunity with just vaccination incentives like tickets to ballgames and free beer. Americans don’t like to be told what to do, and public officials would almost always rather hand out cash than have to punish.

Some even view vaccine mandates as un-American, but they are part of our foundational fabric. During the Revolutionary War, inoculation against smallpox was common in Europe. Because of this, the British Army was largely safe from the disease, but the colonists’ army was not.

Gen. George Washington recognized that mandated mass inoculation was necessary to win the war, though, and told Congress so in 1777. Although he met resistance, his mandate worked. While smallpox outbreaks were common over the next few years and massively affected those who were susceptible to infection, no revolutionary regiments were incapacitated by the disease during the southern campaign, and the mandate arguably helped win the yearslong war.

Today, vaccination rates are stalling in many areas of the United States, and now nearly all Covid-19 deaths are among the unvaccinated. In Indiana, where I live, only half of people 18 or older are fully vaccinated.

Some states, including neighboring Ohio, have engaged in lotteries or prize giveaways in an attempt to entice people to get vaccinated. Those are carrots, or positive behavioral nudges. When it comes to incentives, most people like carrots. Sometimes, though, people need sticks.

When the United States was fighting smallpox long ago, it took mandates to get enough people vaccinated. To eradicate polio, the same was true. Nearly all major infectious diseases in the country — measles, mumps, rubella, pertussis, diphtheria and more — have been managed through vaccine mandates by schools. The result is that the vast majority of children are vaccinated, and in time, they grow into adults who are vaccinated. That’s how the country achieves real herd immunity.

But this process can take decades. Covid-19 is an emergency, and we don’t have that much time.

The mRNA vaccines, made by Moderna and Pfizer-BioNTech, will likely get full approval for use from the Food and Drug Administration soon, which may be necessary for broader vaccine mandates. Although the vaccines are already known to be safe and effective, after being given to hundreds of millions of people, with full approval, more groups will begin mandating that their employees get vaccinated. It’s unlikely the United States can overcome the pandemic without such actions.

The U.S. experience with diseases for which vaccination isn’t mandated is also instructional: In those cases, vaccination rates have remained much lower than desired. The human papillomavirus vaccine approved in the United States, for example, protects against an extremely widespread and often asymptomatic sexually transmitted disease that can lead to cancer. Despite calls to mandate HPV vaccination, it is required for school only in a few states; Washington, D.C.; and Puerto Rico and has never been mandated outside the school environment, where it would do more good.

Although the vaccine was approved in 2006, only about half of teens are currently covered. What’s worse, only 22 percent of 18- to 26-year-olds, who are most at risk for infection, are fully vaccinated. Influenza vaccination is another that has rarely been mandated, and the United States has never achieved anywhere near the rates of protection that health experts would like, even during pandemics.

When it comes to herd immunity, community matters. The rate of vaccination at the national or state level is less important than the rate among people you live or interact with. This means that smaller groups can still take action to protect themselves and those around them from Covid-19. A number of hospitals and health care settings have mandated vaccination because those settings involve higher risk.

Some colleges and universities have also required students, professors and other staff members to be vaccinated before returning to campus. The schools want to return to full classrooms, busy dining halls and a vibrant campus life. They want students to be able to go to football games, events and even parties without fear of outbreaks. The only way to do that is to achieve significant levels of immunity. The only way to do that quickly and safely is through vaccination.

More than 500 colleges and universities in the United States have mandated Covid vaccination so far. My school, Indiana University, where I am the chief health officer, is one of them. Schools like ours believe that the only way to get to the level of safety we need to reopen without outbreaks or worse is to get nearly everyone immunized.

Some private companies have done the same. Many of our health care systems in Indiana have mandated vaccination.

There will be pushback against mandates. (Some students have filed a lawsuit against Indiana University, for example.) But it’s important to understand that mandates don’t mean people will be held down and given shots against their will. The mandate for the Affordable Care Act was a tax. Other mandates, such as those imposed by cruise ship companies, mean you will be unable to take certain vacations this year without vaccination.

And there must be exemptions to vaccine mandates. Some people can’t be vaccinated for medical reasons. Others have religious objections, and such exemptions are protected by law as well as custom. We should all be comfortable with that. To get to herd immunity, even to eradicate diseases, we don’t need vaccination rates of 100 percent. We just need to get to high enough levels that those who are immune protect those who aren’t. And in much of the country, we’re not even close.

When vaccination is the default, most people will get vaccinated. Mandates still aren’t popular; few public health measures are. But they work.