Schools, employers and other big institutions will face enormously difficult decisions as they decide whether to mandate coronavirus vaccinations.

The big picture: The U.S. isn’t likely to see sweeping, government-ordered vaccine mandates, but there could be one-off requirements for specific groups of people. And each will have to balance the benefits against the risk of a backlash that could ultimately prolong the pandemic.

Why it matters: At least 75% of the country probably needs to get vaccinated in order to achieve herd immunity, and widespread skepticism about the vaccine means there’s a chance we won’t get there.

• “I don't think the pathway to a fully vaccinated public is through mandatory vaccinations,” Johns Hopkins epidemiologist Jennifer Nuzzo said. “I think that would actually backfire.”

Where it stands: The early vaccine rollout has sparked new speculation about some kind of system of “immunity passports” — proving you’ve been vaccinated in order to send your kids to school, go back to work or get on a plane. But that's probably not how it will work, at least in the short term.

• For starters, experts generally agree that vaccines won’t be mandatory in almost any setting until they receive full FDA approval, which won’t happen until sometime next year.
• Limited supplies also make mandates untenable: You can’t force someone to get a shot that’s not available to them.

More broadly, many of the institutions that could require proof of vaccination simply may not want to.

• Businesses that are serving customers today — airlines flying full flights, for example — aren’t likely to start setting up new restrictions, accepting less risk than they’re accepting now.
• Employers could require their workers to get vaccinated. But that would be highly controversial, and employees can seek exemptions on religious grounds. For now, more big companies are opting to encourage or facilitate voluntary vaccinations.

“There may be situations where proof of vaccination lets you obviate certain other measures” — like long quarantines or frequent testing — “but I am skeptical they would be mandated or should be mandated,” former FDA Commissioner Scott Gottlieb said.

Yes, but: There are some exceptions to this rule — institutions, most of them private, that may find mandates more appealing.

• Health care facilities have long required their workers to get other vaccines, including flu shots. Experts agree they’re likely to do so in this case, too, and that they should.
• Nursing homes might also want to explore mandatory vaccinations, said Ashish Jha, the dean of public health at Brown University.
• And universities could begin requiring proof of vaccination for students who want to live on campus when classes begin in the fall, Jha said.

The stakes: Each university or nursing home or hospital system that imposes a vaccine mandate is only affecting a small group of similarly situated people. But eventually those small numbers could add up to a significant slice of the country.

• And the more vaccine mandates are perceived as a major force in American life, some experts fear, the more controversial those policies will become — and by extension, the same will happen to the vaccines themselves.

Public schools — the most familiar source of vaccine mandates, and the biggest battleground for debates over those policies — probably won’t require coronavirus vaccinations any time soon.

• Neither the Pfizer nor the Moderna vaccines are authorized for use in children, and they haven’t been tested in children yet.
• Children are also at low risk for serious illness, making them one of the lowest priorities as long as supplies remain limited.
• But this could all be revisited by the time the next school year starts in August or September, when more studies will be completed, supplied will likely be ample and vaccines likely will have full FDA approval.

One big question: We still don’t know whether the initial COVID-19 vaccines simply prevent you from getting sick, or actually stop the virus from spreading.

• If they don’t stop transmission, the case for requiring them is weaker — especially for groups, like children, who are at a low risk of serious infection to begin with, Nuzzo said.