The theory behind a health pass—or what many think of specifically as a vaccine passport—is fairly straightforward. Individuals would be able to carry their personal health data on mobile devices. When prompted, they could scan a QR code (or something similar) at the doctor’s office, a sporting event, or the airport to show proof of vaccination status.

It’s not theoretically complicated, but implementation of the technology is.

There are a plethora of concerns about data privacy, methodology, and—in the case of COVID-19—limited access to vaccines or even polarization over the vaccines themselves. These were a handful of issues raised Tuesday at a virtual Brainstorm Health panel discussion, hosted by Fortune.

Barriers aside, the vaccine passport project has drawn “a huge amount of interest” both in the U.S. and abroad, according to Dakota Gruener, executive director of the ID2020 Alliance, a global partnership to build a universal digital ID. 

People are anxious to return to normalcy, Gruener said, and commutable, universally accepted proof of vaccination status could help speed up the process.

As for the best way to go about it, there are two key details that need to be addressed, she said. There must be adequate privacy protections in place, giving individuals the autonomy to choose what sort of health data they share. The passes would also need to be widely accepted across industries and countries.

Some companies, including IBM Watson Health, have been working to develop a solution. It was a project underway “many years before the pandemic,” according to Eric Piscini, global vice president of payer and emerging business networks at IBM Watson Health. Other potential uses for the technology could include proof of infant vaccines, portable medical records, or proof of college degree or training courses, Gruener said.

But vaccine passports in particular have emerged as a more immediate and urgent use case.

IBM Watson Health’s pass was made to help employers address workplace safety, reentry, and facilities management by enabling individuals to share test results or on-site temperature scans via a digital wallet.

The digital wallet is built on blockchain technology to address widespread industry concerns over data privacy and potential vulnerabilities in the case of a data breach.

“Blockchain technology gives us the option to provide verification of [vaccination] status without correcting or keeping any of the information on our platform,” Piscini said.

Beyond privacy concerns are layers of differing and evolving requirements from the federal government, state public health departments, and individual county health departments in the U.S., according to Jonathan Dordick, institute professor of chemical and biological engineering at Rensselaer Polytechnic Institute.

“That makes life very difficult when you’re trying to figure out what kind of pass exists, what kind of information can be put on the pass, and when you have a test, what does that test mean,” Dordick said.

Additionally, requirements—and access to vaccines—vary internationally.

“I think we are starting to see those first movers, but we still have some major markets like the U.S. and the U.K., for example, that really need to come together around a standard for opening up,” said Sharon Pinkerton, senior vice president of legislative and regulatory policy at Airlines for America, a trade association and lobbying group for the North American airline industry.

While the logistics may be unclear, the technology is there, according to Piscini. It’s the implementation and the education around it that still need some attention, he said.

More health care and Big Pharma coverage from Fortune:

• 12% of the world’s population has received a COVID vaccine. See how your country is doing
• England’s reopening is officially in limbo, serving up a cautionary tale for countries on the vaccination forefront
• What we know about COVID vaccines, heart inflammation, and its implications for drugmakers
• India needs Pfizer vaccines—but company demand for legal protection is holding things up
• Commentary: To vaccinate our economy, boost support for the NIH