Its creator, North Carolina-based tech company CastleBranch, says the digital vaccination card is the first to become available to the public. Neither should advertisers or corporations.”CastleBranch is just one of many companies attempting to distribute COVID “passports.” Earlier this month, the company launched its physical identification card that travelers can carry as proof of COVID vaccination. Chicago-based United Airlines announced Monday that it plans to release an update to its travel app that allows COVID passport compatibility. United is the first major airline to move toward accepting such a document and has said it’s willing to accept COVID passports from different companies. Digital-liberty experts are also imploring extreme caution when gathering sensitive health data from a massive portion of the population.