As vaccination rollouts gather pace around the world, attention is now turning to vaccines of another kind: vaccine passports.
Last week, the International Air Transport Association announced the launch of its new digital travel pass as "the way forward" in resuming quarantine-free international travel.
The app, which is being tested by 30 carriers, will allow governments and airlines to collect, access and share encrypted information related to passengers' Covid-19 test and vaccination status prior to travel.
The International Chamber of Commerce and the World Economic Forum have created similar apps — ICC AOKpass and CommonPass — to allow travelers to document their medical status electronically. Countries such as Denmark and Sweden are launching their own health passports, and even tech giants are looking to get in on the act.
What are digital health passports and will they facilitate a return to the skies this year?
Also known as a digital health pass, a vaccine passport is digital documentation that an individual has been vaccinated against a virus, in this case Covid.
Stored on a phone or digital wallet, the data is typically presented as a QR code and also can show if a person has tested negative for a virus.
Such documentation is not unprecedented. For decades, people have had to show physical "yellow cards" as proof of vaccination against diseases like cholera, yellow fever and rubella when traveling to certain countries.
However, this marks the first time that the industry has rallied behind an electronic alternative designed to improve verifiability and circumvent some of the hold-ups caused by paper counterparts.
"Just imagine the scene if 180,000 people present a piece of paper that needs to be checked and validated," said Mike Tansey, a managing director at Accenture, referencing the pre-Covid number of daily passengers at Singapore's Changi Airport.
Tansey, who leads Accenture's APAC travel and hospitality division, has been working with some major airlines on their digital health pass strategies, including three in the U.S. and several across Asia- Pacific.
He told CNBC's Global Traveler that those plans have "accelerated" since the vaccine rollout, and for him, the need for such passes is clear.
"The obvious answer is yes, we do," said Tansey, when asked if we would need digital health passes to resume travel.
He called debates a "red herring."
"Governments may not say that you have to have one, but the implications of not will be so ridiculous that travel won't be worth it," he said, referring to extensive testing and "draconian" quarantines.
Tansey is not alone. Other experts agree digital health passports may be the quickest and most effective way of resuming international travel.
Jase Ramsey, professor of management in Florida Gulf Coast University's Lutgert College of Business, agreed the probability of adoption was "very high." But he noted that concerns around security and personal data may leave consumers less willing to adopt digital health passes than their physical alternatives.
"As with any app that stores health records, there will be privacy and fraud concerns," said Ramsey.
Accredify is one Singapore-based document accreditation firm whose technology is being used under the Singapore government's mandated pre-travel Covid-19 health screenings. It claims that the appeal of digital accreditation systems — such as its own, which is based on the blockchain — is that they are tamper-proof and therefore unable to be falsified.
"Medical documents stored privately and securely on the app are accessible only to users, giving them the decision of who to share their medical records with and when," a spokesperson said via email.
Resistance from travelers may be overstated. A recent study from travel news site The Vacationer found that 73.6% of Americans surveyed say they would use a Covid health passport or app so airlines and border authorities can check their vaccination status and test results.
The success of digital health passports will hinge on the effectiveness of vaccines. Little is known about whether vaccines prevent the spread of Covid, though research is underway.
The World Health Organization has urged caution toward health passes, telling authorities and travel operators not to introduce proof of vaccination as a condition for international travel.
"This is because the efficacy of vaccines in preventing transmission is not yet clear, and global vaccine supply is limited," a WHO spokesperson said.
Coordinating the various existing and pending vaccine passports on the market, and ensuring users' certifications are linked to verified and approved medical facilities, will prove a major challenge.
"In order for vaccine passports to be an internationally practical tool, there will need to be a standardized platform that crosses all boundaries — such as the current passport system," said Dr. Harry Severance, assistant professor at Duke University School of Medicine.
The WHO is working with agencies including the International Air Transport Association and the International Civil Aviation Organization to develop standards for digital vaccination cards. It added that its position on health passes will "evolve as evidence about existing and new Covid-19 vaccines is updated."
Then, of course, there are the social, legal and political ramifications of a system based on inequitable global access to vaccines and technology.
Approximately 3.6 billion people globally cannot access the internet, according to the WHO, and more than 1.1 billion cannot officially prove their identity. For many, paper passes will remain essential.
"People from different countries, regions or communities may not have access to vaccines or Covid-19 testing," said Dr. Sharona Hoffman, a bioethics professor at Case Western Reserve University's School of Medicine, noting that low-income countries may not receive vaccinations until 2023 or beyond. "A policy that prevents them from traveling or obtaining other services because of that could be discriminatory and exacerbate socioeconomic disparities."
Such systems could also set a precedent among other groups similarly eager to reopen, such as restaurants and events venues. Indeed, Israel has already created a "green passport" to give vaccinated citizens access to public venues.
This week, some U.S. states moved to lift mask mandates, which could exacerbate this issue.
"As one community moves in this direction, many, many more will follow. As such decisions roll across the country, you may find that vaccine 'carding' is becoming a standard," said Severance.
Ultimately, the resumption of international travel will depend as much on countries' willingness to reopen as it does on the travel verification technology in place.
In Asia-Pacific, where borders largely remain closed to tourists, governments may tend toward bilateral agreements, or "travel bubbles," with select neighbors before opening up more broadly, said Accenture's Tansey.
"The reality ... is we're still six months away from any meaningful air travel," he said. "It's only going to be agreements with one or two places at a time."
Still, with much of the technology in place, and with society moving toward an ever-more digitized future, developments made today in digital health passports could leave the travel industry — and society — better prepared for any potential turbulence ahead.
"If we evolve to an internationally recognized system of health passports (or) monitoring etc., that will be one facet of a downstream preparedness system that will possibly allow us to survive an upcoming pandemic, that may have worse dynamics than Covid-19," said Severance.