With millions being vaccinated against Covid-19 every day, some political and business leaders are suggesting nations can help get life back to normal by rolling out a so-called vaccine passport: an easily accessible and verifiable certification that a person’s been inoculated. Private companies are already beginning to look at making shots mandatory for people who want to get on planes, cruise ships or attend events such as concerts. A handful of projects from governments, private firms and international associations are currently underway. But the idea raises scientific and ethical questions.

1. What’s the idea behind vaccine passports?

In this photo illustration a view of the vaccination card

The yellow card

At the moment, many countries and airlines require proof that international travelers aren’t infected with SARS-CoV-2, but regulations vary from place to place and so far there’s no systematic requirement that people be vaccinated. The idea of a vaccine passport would be to create an updated version of the so-called yellow card, more formally known as the International Certificate of Vaccination or Prophylaxis, a World Health Organization-approved booklet documenting your past inoculations. Given the prevalence, contagiousness and devastation of Covid-19, many are suggesting the need for a more modern, digital and secure record. Ideally, it would provide proof of vaccination status and document recent virus test results, which would both reassure border agents and safeguard fellow travelers or event-goers. The demand for such proof has led to falsified and counterfeit paper versions of vaccine certificates, according to WHO spokeswoman Margaret Harris.

2. Who’s considering requiring proof of vaccination?

A handful of companies have begun mandating — or hinting they will eventually require — proof of vaccination, foreshadowing what could become a more common practice. U.K.-based Saga Cruises, part of an industry that was a prominent early victim of the pandemic, is already requiring that passengers present proof they’ve been fully vaccinated before sailing. The chief executive officer of Australian airline Qantas Airways Ltd., Alan Joyce, has said his company plans to require international travelers entering or leaving Australia to present proof of vaccination before boarding. Joyce said he expects other carriers to do the same. Ticketmaster, which sells tickets to live events, has said it’s exploring options for event organizers who may want to require attendees to present proof of inoculation; for instance, ticket-holders might be able to link their vaccine record to their digital ticket.

3. Will countries require proof of vaccination for entry?

It’s possible, especially as more people get vaccinated. So far, the WHO doesn’t support it. Yet the agency also recommends against imposing travel restrictions in response to pandemics, and that advice has been widely ignored as countries slapped Covid-related flight bans on other nations. Under the International Health Regulations, which are legally binding on the 196 states that are party to it, only one vaccine — against yellow fever — is endorsed as a requirement for entry into countries. In early February, the WHO recommended against adding Covid vaccines for two reasons. First, it’s not clear such requirements would stop the cross-border spread of SARS-CoV-2 since it’s not known yet how well the shots prevent people from transmitting the virus, even if they aren’t sickened by it. Second, Covid vaccines are in limited supply. Last year, the agency discouraged the introduction of “immunity passports” based on the presence of antibodies, since there was no evidence people with antibodies couldn’t be re-infected.

5. Who’s developing vaccine passports?

There are a number of private firms, organizations and governments backing or attempting to create a workable vaccine passport. With financial support from Innovate U.K., technology companies Mvine and iProov have begun live-testing a Covid-19 immunity and vaccination passport designed to be compatible with the U.K.’s tiered approach to managing the health crisis, under which different parts of the country are under varying levels of restrictions. The World Economic Forum and the Commons Project, alongside the Rockefeller Foundation, say they have convened more than 350 public and private sector leaders from 52 countries to create a technology platform called CommonPass that aims to provide people with a “secure and verifiable way to document their health status as they travel and cross borders.” The Israeli government offers a “green passport” for those who have been vaccinated, while the International Air Transport Association is working on a travel pass that would enable air passengers to comply with health-screening measures required at their destinations.

6. Apart from barring the unvaccinated, how might border officials use vaccine certificates?

Vaccine passports or certificates could be used as a way to loosen up current rules that bar certain travelers, require arriving passengers to test negative for the virus and compel them to quarantine upon arrival. Infectious-disease physicians from a dozen countries proposed in mid-January that people who’ve completed a full course of Covid vaccination be allowed to travel freely for a specified period — probably six months — until more is known about the duration of protection the inoculations provide. But there are still political issues. The 27-nation European Union is looking into possible vaccination certificates as member countries struggle to accelerate inoculations and revive cross-border travel. With tourism-reliant Greece pressing for an EU-wide system and Germany leading a group of countries urging a go-slow approach, deliberations are likely to be drawn out. Among the concerns in the EU is that creating a category of travelers with special privileges could undermine the free cross-border movement of people — a basic principle of the bloc.