Many countries and several U.S. states have employed digital vaccine passports, touting them as a handy way for restaurants and other businesses that require COVID-19 vaccination to vet patrons. California is one of those states, and its Department of Technology director said last year that it's great for the patrons, too, contending the system is "really for the purpose of empowering individuals to access the official copy of their own immunization records." Advertisement - story continues below But privacy advocates, including the ACLU, have raised concerns. And some critics have argued that such technology in the hands of a tyrannical...