Masked passengers line up at Ronald Reagan National Airport just outside Washington, DC.

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As international travel becomes possible again after more than a year of largely staying at home, proving your COVID-19 vaccination  status (or maybe just a negative COVID-19 test) will be part of globetrotting. Some countries, including those in the European Union and nations with economies dependent on tourism, are pushing ahead either with real vaccine passport plans or allowing vaccinated visitors to skip quarantine requirements for entry. The private sector, most notably cruise lines and airlines, is also eagerly climbing aboard. But the idea is not without controversy.   

Proving you're vaccinated to travel abroad isn't a new concept -- some countries have required yellow fever vaccines for years -- but doing so for COVID-19 would be on a far grander scale than ever before and would present immense logistical challenges. Passport skeptics also predict they could result in discrimination and fraud, encourage risky behavior in the face of new coronavirus variants, and be a privacy minefield. As the debate continues, here's what we know.

This story has been updated with new information. 

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Vaccine passports for COVID-19: How they'll be a part...

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How would a COVID-19 vaccine passport work?

Despite its name, the vaccine passport (or vaccine certificate) likely wouldn't be like the little booklet you present to immigration officials when you cross an international border. Rather, the most probable concept is a mobile app with a scannable barcode that shows your vaccination status. The app could also allow you to check entry requirements for a country (possibly after uploading your itinerary) and hold the status of your last COVID test, and maybe other health information. For people without smartphones, some proponents are pushing for an alternative paper version. 

The multiple apps in development could verify your vaccination a few ways. Perhaps you could take a photo of a paper vaccination certificate, but that method opens the door to possible forgery. A better option would link apps to databases that hold vaccination records. In the US, that data is held not at the federal level, but by individual states.

Is a vaccination passport being used now?

Not yet, at least on a cross-border basis. But Israel, which is leading the world in vaccination rates, has launched a "green passport" that gives holders access to places like gyms, theaters, hotels, concerts and synagogues. New York state has announced an app called Excelsior Pass, which shows your vaccination proof or the results of a negative COVID-19 test (you must also show a photo ID). 

Is there just one version of a vaccination passport in development?

Currently, a few businesses and organizations are working to create passports. Here's a partial list.

One is the International Air Transport Association, a trade group based in Montreal that represents 290 airlines worldwide. The IATA is developing an app called Travel Pass that would let users upload documentation to prove vaccination status. It would also allow passengers to check health entry requirements for countries they plan to visit and find COVID testing centers -- either before they leave for a trip or upon arrival. Eventually, the Travel Pass could incorporate biometric information, such as a thumbprint or facial recognition, to prove a person's identity. 

The IATA says 23 airlines, including Qantas, Singapore Airlines, Virgin Atlantic and the parent company of British Airways, are testing Travel Pass. The organization says airlines would have the option of integrating the data into their own apps. Digital Health Pass, which enables "organizations to verify health credentials for employees, customers and visitors entering their site based on criteria specified by the organization." 

Clear, the registered traveler program that allows you to speed through security at US airports, is pushing its own app's 

Other possible apps include the , and .

The IATA is developing Travel Pass for its member airlines. 

Won't it be confusing to have several apps?

A lack of standardization would be a burden for everyone. Some apps, for example, could request more information than others or could work in different ways. Another potential problem could be countries and airlines accepting only some apps, forcing you to upload your vaccination records multiple times. We'll have to see how that plays out, but it could be  and sort out the mess (more on that later).

Will all vaccines qualify? 

No, which also could make things complicated. The European Union has said it will only accept the Pfizer, Moderna and Johnson & Johnson vaccines for its vaccine certificate plans (see next section). Other countries may decide to accept Russia's Sputnik V and China's Sinopharm vaccines, as well.  

Which countries will use use vaccine passports?

It's a broad coalition, with much of the push now coming from Europe. Popular tourist destinations such as Greece, Portugal, Croatia, Spain and Cyprus are especially eager.

On March 1, EU Commission President Ursula von der Leyen that the EU would present a legislative proposal this month for that would include proof a person has been vaccinated, has received a negative test result or has recovered from COVID-19. Two weeks later on March 17, the European Commission  (PDF) for resuming free travel within the bloc for EU citizens and residents with Green Passes, which could be ready by June. 

At the moment the , but that will likely change by June. On May 3, European Commission spokesman Adalbert Jahnz  to  from the US and other countries to visit the EU -- as long as they've been fully vaccinated. How you'd prove status, though, is still under review.

Outside of the EU, UK Prime Minister Boris Johnson has said his government their use. and  are also advocating for vaccine passports, as like Thailand and .

Keep in mind, though, that some countries are still restricting visitors regardless of vaccination status. And many places, including 

What has the US government said?

As part of aimed at curbing the pandemic, President Joe Biden directed his Cabinet to assess the feasibility of linking COVID-19 vaccination to the current International Certificates of Vaccination or Prophylaxis used by the WHO (more on that later). It's clear, though, that there will be no national mandate for using them.

In , White House press secretary Jen Psaki said the private sector would likely drive domestic use of vaccine passports. "There are lots of ideas that will come from the private sector and nonprofits," she said. "We welcome those. But our focus from the federal government is on getting more people vaccinated, and that's where we feel we can use our resources best." , "There will be no federal vaccinations database and no federal mandate requiring everyone to obtain a single vaccination credential." 

Andy Slavitt, acting administrator of the Centers for Medicare and Medicaid Services,  in a March 29 briefing. "We view this as something that the private sector is doing and will do," he said. "What's important to us -- and we're leading an interagency process right now to go through these details -- are that some important criteria be met with these credentials." That criteria includes equitable access to the passports (such as for people who don't own smartphones) and securing the privacy of user information.

Have any places already changed entry requirements for vaccinated travelers?

Yes. Iceland was one of the first countries  vaccinated visitors to skip testing and quarantine requirements. It's been joined by  including Belize, Croatia, Ecuador, Estonia, Guatemala, Montenegro and Seychelles. That list .

In the US, Hawaii that will allow travelers who have been vaccinated to skip COVID-19 testing or quarantine. 

Does the US require a COVID vaccination for tourists?

Though the US already  to enter the country, it a COVID vaccination. Visitors to the US and returning US residents against anything, though immigrants .

Where is the pushback coming from?

In the US, vaccine passports have already  -- with Republican elected officials in particular decrying any use in domestic settings as a violation of personal freedoms. One of the loudest critics has been Florida Gov. Ron DeSantis, who  April 2 banning businesses and government agencies in the state from requiring vaccination passports. But that order , a powerful force in the Florida tourism sector (see later section about the private sector).

And around the world, the idea has yet to gain traction in developing countries with less access to the vaccine or with economies not dependent on tourism. 

What does the World Health Organization say?

Though the WHO is exploring how a vaccine passport might work, it said, "At the present time, it is WHO's position that national authorities and conveyance operators should not introduce requirements of proof of COVID-19 vaccination for international travel as a condition for departure or entry, given that there are still critical unknowns regarding the efficacy of vaccination in reducing transmission." 

The WHO confirmed that opinion in following an April 15 meeting. The organization does not recommend that countries "require proof of vaccination as a condition of entry, given the limited (although growing) evidence about the performance of vaccines in reducing transmission and the persistent inequity in the global vaccine distribution."

Are cruise lines interested?

Very much so. Cruise lines are motivated to support the use of vaccine passports given that cruise ships like the  were major coronavirus hotspots when the pandemic began (and less recently for ). 

"Cruise ships had a very, very difficult problem to solve," said Terry Jones, the founder of Kayak and Travelocity and a former CIO of American Airlines. "And they're a small microcosm of a lot of people. And so to get people to feel safe again, it simply makes sense."

Royal Caribbean announced on March 1 that it  and that all passengers 16 years and older will have to be vaccinated. It also has announced from  and  will be open only to vaccinated crew and passengers. It's not a stretch to assume that such a mandate will be enforced across all of the company's ships. 

That's the case with Norwegian Cruise Lines, which announced April 6 that all passengers booked on cruises through Oct. 31 . Other cruise lines  with varying requirements of their own, including Cunard, Celebrity, Princess, Seabourn and Viking. Keep in mind, though, that the  for cruise lines to begin sailing from the US. At present, a vaccination requirement for passengers is not among them.

Qantas said it will require international passengers to be vaccinated. 

What about airlines?

Airlines, led by the IATA, cruise lines and others in the travel and hospitality industries are big supporters. Qantas, for example,  to Australia to have a vaccine to fly. Given the country's  and success in , it's not surprising. The CEO of Qatar Airways  the idea. Among the airlines using CommonPass on a trial basis for select flights are United, Cathay Pacific and JetBlue, Lufthansa, Swiss International and Virgin Atlantic.

There is a big incentive for airlines to endorse the idea of a vaccine passport for international flights. Keep in mind that airlines are responsible for ensuring passengers have the correct documentation to fly to any country before boarding a flight. In a sense, that makes an airline check-in desk the equivalent of a border crossing. And if an airline happens to fly someone to a country they can't enter because they're not vaccinated, the carrier is responsible for flying them back home at its own expense. 

Terry Jones said it's unlikely that could happen for domestic flights, though that could change (see video). "The President . So, there could be some of that going on," he said. "I think it simply makes sense."

What are the arguments in favor of a vaccine passport?

Advocates say they could:

The problem, though, is that these reasons aren't perfectly in line. So, which will be prioritized? That's something we'll have to decide.

What are the arguments against a vaccine passport?

There are a few critical ones here, as well:

If I'm not vaccinated, could I get by with a negative COVID test result?

Possibly. That would be the case with the EU's Green Pass. But we'll have to wait and see whether other countries or businesses adopt such a policy.

The WHO Yellow Card lists a bearer's vaccination status. 

Some countries require vaccines for other diseases like yellow fever. How is this different?

A vaccination as a requirement to enter a country is not a new concept. The affected diseases include not just yellow fever, but also meningitis and polio. Travelers can record their shots and prove vaccination status with the WHO's (also called a ) [PDF], which is a vaccine passport. Or as Jones put it, "This is simply a digital representation of that time-worn idea."

COVID-19 is different because it's happening on a vastly wider scale than something like yellow fever. Only a handful of countries, all in equatorial Africa, require a yellow fever vaccination for all travelers. And other countries -- like China, Australia, South Africa and Colombia -- only require it if you're arriving from a country with a yellow fever risk (the WHO of vaccination requirements by country).

Why not use a paper passport?

Advocates say there are a few reasons to go digital. Paper passports would be more subject to forgery, and they'd be more difficult to replace if lost, stolen or damaged. It's also likely that border officials would be able to check digital passports quicker than they would paper certificates. That would help at busy international airports where multiple flights with hundreds of people each can arrive within minutes of each other.

Once I have one, can I stop wearing a mask and social distancing?

No. Social distancing and are still absolutely essential for fighting the spread of the virus and protecting the health of yourself and others. And they'll remain that way for many months.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.