Vaccine passports are pitched as alluring route back to near-normality from the COVID pandemic.

People could show these certificates, in digital or paper form, to authorities and businesses to prove they have had the jab, a negative test, or that they have recovered from COVID and are presumed to be immune. It would, in theory, help contain the spread of the virus and reassure those who are worried about mingling with crowds.

In countries that restrict international travel, vaccine passports could help kickstart international flights and tourism. They could also allow a safer and quicker opening of places where people typically gather in large numbers such as entertainment and sports venues.

But some people oppose the idea of vaccine passports on privacy and civil liberties grounds. In no way, they say, should anyone have to carry any ID or share sensitive health data with companies or the government.

Here’s everything you need to know about vaccine passports.

What are vaccine passports?

Typically, vaccine passports involve downloading a smartphone app and adding a certificate with a QR code showing you have been vaccinated or information about your latest COVID test. Immigration officials along with airport, stadium, and restaurant workers can then scan the code.

People who don’t have smartphones may be able to print the QR code and carry a paper version.

Event organizers and travel operators could make vaccine passports mandatory. Several cruise operators, such as Saga Cruises, have said they will require passengers to be fully vaccinated when they resume sailing in the summer.

Most governments have yet to say whether they will make vaccine passports a requirement to enter their countries, but in some cases, the alternative to showing one may be quarantine.

Where are vaccine passports being used?

In the U.S., where nearly 100 million people or 30% of the population have received at least one dose of vaccine, the state of New York is leading the way in introducing vaccine passports. Gov. Andrew Cuomo last week announced a voluntary scheme, known as Excelsior Pass, a free platform developed with IBM. This allows people to print out their vaccination certificate or store it on their smartphone using the Excelsior Pass Wallet app, in the same way they do with mobile airline boarding passes.

Each pass will have a QR code, which participating businesses and venues can scan to verify that the holder has been vaccinated or has had a negative COVID test. New York state envisages the scheme being used by major stadiums and arenas and for large events such as wedding receptions. Major venues that have already announced they will begin using the technology in the coming weeks include Madison Square Garden in New York City and the Times Union Center in Albany.

Hawaii is reported to be looking into the use of vaccine passports, especially for inter-island travel. Further afield, Israel, which has fully vaccinated more than half its people, has introduced a vaccine passport, called a Green Pass, that is needed to get into gyms, swimming pools, hotels, cafes and restaurants, cinemas, theaters and sports stadiums.

What’s planned?

The Biden administration says it expects vaccine passport initiatives to be driven by the private sector, although the federal government will provide guidance. White House Press Secretary Jen Psaki said this week that the U.S. government would make recommendations following an interagency process that is looking into vaccine verification. But she said there would be “no centralized, universal federal vaccinations database and no federal mandate requiring everyone to obtain a single vaccination credential.”

Many other vaccine passport schemes are being studied or developed. For example, a coalition that includes Microsoft, Oracle, and Salesforce in January created the Vaccination Credential Initiative with the aim of letting people store an encrypted digital copy of their immunization credentials in a digital wallet of their choice.

Meanwhile, The Commons Project, a non-profit that builds digital services, the World Economic Forum, and other partners are working on CommonPass, an app that lets people access their lab results and vaccination records.

The International Air Transport Association (IATA), a trade association for the world’s airlines, is working on its Travel Pass, an app that would tell passengers which tests and vaccines they need before they travel to a particular country. Passengers would be able to use the app to share their tests and vaccination certificates with authorities. IATA’s web site lists 22 airlines that are testing the app, including Etihad, Emirates, Qantas and Virgin Atlantic.

The European Union’s executive body has proposed a voluntary “Digital Green Certificate” that would prove that a person has a COVID-19 vaccine, had received a negative test result, or had recovered from the disease. The certificate, which will include a QR code, would be available, free, in digital or paper format.

China has launched a vaccine passport system as a free app, built on China’s Tencent-owned WeChat messaging service. Meanwhile, Japan and South Korea also plan to issue digital vaccine passports.

These governments are making vaccine passports available in hopes that it will make it easier for their citizens to travel to other countries. But that depends on other countries accepting them as valid proof of vaccination, which would have to be negotiated.

Fierce opposition

Critics of vaccine passports say they discriminate against those who don’t have access to vaccines or those who refuse to take them, effectively forcing those people to be excluded from travel or socializing. There are also fears that paper certificates could be forged or that health data shared with Big Tech could be hacked.

The World Health Organization said in February it opposed making vaccine passports a requirement for international travel because of a lack of data about how effective vaccines were in reducing transmission of the disease. With poorer countries’ vaccination programs already lagging wealthier countries, “introducing a requirement of vaccination as a condition for travel has the potential to hinder equitable global access to a limited vaccine supply,” the WHO said.

In Britain, more than 70 lawmakers from across the political spectrum have launched a campaign against requiring vaccine passports for entry to pubs and nightclubs, a policy that the government is considering.

In the U.S., the strongest opposition has come from conservative politicians who see vaccine passports as an unwarranted intrusion into private lives. Florida’s Republican Gov. Ron DeSantis said this week that it was “completely unacceptable” for either the government or the private sector to require people to show proof of vaccination “to just simply be able to participate in normal society.

Rep. Marjorie Taylor Greene, a Georgia Republican, also slammed the idea of private companies demanding vaccine passports as “Corporate Communism” on Twitter. She