But a lot is happening behind the scenes to expand these uses, some of it very quickly. Governments, airlines, employers, universities, and many other groups are intensely debating how and why people will need to show verified health records. Some of the terms being thrown around are confusing, like “vaccine passport.” In some scenarios, your records might function like an actual passport—think of arriving at the airport in a new country, pulling out your smartphone, and scanning a digital record of your vaccination or negative test. But those records could also act like a work authorization at your job, or a pass to get into restaurants, bars, and shopping malls. Proponents argue that digital health credentials could help us get back to “normal,” but there are lots of roadblocks to making these ideas a reality, both on a medical and technical level. Immunization doesn’t mean safety While several vaccines appear highly effective at preventing symptoms of covid-19, we don’t know whether they stop people from catching and spreading the virus asymptomatically. Trials of the Oxford-AstraZeneca vaccine suggested it may limit transmission from asymptomatic carriers, but Pfizer and Moderna’s trials didn’t regularly test participants for the virus if they didn’t have symptoms. More data is needed to prove conclusively that vaccination prevents you from giving covid-19 to other people, and how long immunity lasts. It’s also important to remember that what’s true for one vaccine may not be true for another. Without these crucial pieces of information, vaccination credentials only prove that you received a vaccine on a particular date—not that you do not have and cannot catch the disease. In the meantime, a negative covid test remains the best evidence that you’re not contagious. And since tests are far from perfect, you should still follow public health guidance about limiting spread whenever you can. Digital records help combat fake information There is already a booming black market in fake test results that is diminishing trust in printed records and driving demand for cheat-proof digital documents. Many governments, as well as airlines and other businesses are trialing or in talks to build “health pass” apps, which let users ask participating labs and health systems to send authenticated test results and other data straight to the app, bypassing verification concerns. There are a lot of players in the field, including IBM, the Commons Project, and the Covid Credentials Initiative. They’re coming at the problem from different angles but are ultimately chasing the same goal: let people share required information about their health, while protecting other private information. Yet it’s still too early to rely on any of these for a fast and widespread solution. Linking up systems is very difficult Health-pass makers are mostly focused on test results for now, but any of those technologies could work just as well for vaccine records, if all the systems worked together. Unfortunately, that’s a much bigger challenge than signing deals with a couple of big testing companies. Connecting any systems across borders means navigating a patchwork of languages, databases, and privacy laws. Even in the UK, where the National Health System maintains a database of vaccine recipients, the government has put any talk of vaccine “passports” on hold.