Imagine a future when a single document determines whether you work, play or travel.

That scenario – a system of “immunity certification” that grants privileges to those vaccinated against the COVID-19 virus – is now being deliberated by a growing number of global businesses and governments, anxious to control the disease and also restore the economy.

The debate comes at a time when millions of people, slowly but surely, are getting vaccinated and are restless to return to their pre-pandemic lives. Yet many millions of others are forced to wait.

“People are starting to ask: ‘Why should I be subject to restrictions if I don’t actually pose a risk to other people?'” said David Studdert, a professor of medicine and law at Stanford University.  “One way or another, it seems like ‘immunity certification’ is coming our way.”

While the World Health Organization and U.S. Centers for Disease Control and Prevention are unlikely to embrace such a strategy, others are already adopting it.

Next month, the National Football League is inviting 7,500 special guests to the Super Bowl: health care workers who can prove they’ve received two doses of the COVID-19 vaccine.

Overseas, the European Commission (WHO) is seeking to ease safe travel within its borders through the creation of vaccine certificates. While they would initially be used only for medical care — helping travelers who suffer any vaccine-related adverse events — there will likely be other applications in the future, according to the Commission’s Jan. 19 report.

“As more people are vaccinated, the documentation and mutual recognition of vaccination become of utmost importance,” the report concluded.

Already, the nations of Cyprus, Romania and the Seychelles are allowing vaccinated visitors to skip the nations’ quarantine and testing requirements. In Chile, citizens that have recovered from COVID-19 — gaining antibodies that give them a natural form of immunity — have been given “virus free” certificates.

The concept is also gaining traction in the hard-hit airline and cruise industries. Last week, the British cruise operator Saga Cruises announced it will require all passengers to be fully protected when sailing resumes in May. Australia’s Qantas Airways says it is considering requirements that international travelers be vaccinated before boarding the company’s planes.

Americans are deeply divided on such a strategy, according to a new survey published this week.

The research, conducted by Studdert and Mark Hall of Wake Forest University, found a nearly 50-50 split in those who support or oppose so-called “immunity privileges.” And opinions didn’t follow the normal political contours; liberals and conservatives took both sides.

In some respects, a COVID-19 certificate isn’t all that different than today’s yellow fever card, which proves vaccination against that deadly virus for entry into nations where the disease is still raging.

And proof of vaccination against other pathogens, such as TB and influenza, is already mandatory in certain professions, such as health care. In California, youngsters are required to be vaccinated against childhood diseases to attend school.

But it’s been more than a century since America restricted basic freedoms on the basis of someone’s antibody status. The last time this strategy was deployed was during the 19th century, when immunity to yellow fever divided the residents of New Orleans, dictating who you could marry or where you could work. That experiment exacerbated cultural inequalities and tore the city’s social fabric.

There are both practical problems and ethical objections to immunity certificates, said Natalie Kofler, founder of the global initiative Editing Nature and adviser for the Scientific Citizenship Initiative, Harvard Medical School in Boston.

For one, no one yet knows if vaccination prevents transmission, especially among asymptomatic people, she said. And there’s unfair access; the wealthy and powerful are more likely to get a vaccine than the poor and vulnerable. Restricting work, concerts, museums, religious services, restaurants or political polling sites only to those vaccinated could disenfranchise many people.

There are other challenges, say experts. Would a certificate allow all vaccines, including those not approved by the FDA but made in China and Russia? What about people who only get one dose? If someone can’t be vaccinated, due to risk of rare but real side effects, will they face discrimination? What about the 5% of people who are vaccinated, but not protected?

“Over time, it is likely that a vaccine certification could both be scientifically robust, as well ethically permissible,” Kofler said. “But we’re not there yet.”

Before a COVID-19 vaccination certificate can become compulsory for travel the world over, it would have to be part of the World Health Organization’s International Health Regulations.

For now, the WHO has discouraged the issuance of such certificates, saying their validity cannot be guaranteed and may exclude poorer nations. But it is designing an international digital vaccination card that will provide a framework for nations, with rigorous standards.

The U.S. Centers for Disease Control and Prevention already issues a card to Americans who are COVID-19 vaccinated, verifying the date and type of inoculation. But experts say it seems unlikely to embrace any strategy that mandates use of the card — instead opting to provide oversight, regulating the fairness or accuracy of this approach.

To prepare, some companies are developing technologies that allow recovered or vaccinated individuals to verify their status.

The International Air Transport Association is building a digital passport called Travel Pass, a mobile app that will hold a traveler’s COVID-19 health status.

Two tech giants – IBM and Salesforce – are designing a blockchain-powered smartphone app called IBM Digital Hall Pass that lets companies and venues customize what’s required for entry, such as COVID-19 test results, temperature checks and vaccination records.

“Now, as testing becomes more widespread and vaccine distribution gets underway, we (will) help organizations verify an individual’s vaccine status and any other relevant health credentials,” said Paul Roma, general manager of IBM Watson Health.

Additionally, a major coalition called the Vaccination Credential Initiative is creating an encrypted health card, called CommonPass, that can be stored in any digital wallet or a paper QR code. Its members include Microsoft, Oracle, the Mayo Clinic and the two largest electronic medical record companies, Cerner and Epic

To coordinate these many efforts, the Linux Foundation is working to help develop a set of universal standards for vaccine credential apps.

Could such a tool become a part of everyday life, allowing people back to the job, classroom, concert hall, stadium or movie theater?

It’s still too soon because so few people have been vaccinated, according to Studdert and Hall. But as numbers climb, it may be inevitable.

“This is sort of a logical and expected way to behave,” said Hall. “The question is: Do we let things roll on? Or do we help steer the course?”