The idea of issuing “immunity passports” to individuals with covid-19 antibodies continues to attract both interest and controversy. Estonia and Chile are both moving forward with plans to test their own immunity-passport programs, and top infectious disease expert Anthony S. Fauci says U.S. officials have discussed the idea too. The private sector is likely to beat the federal government to the punch. Start-ups like FaceFirst and Onfido are pitching the idea of app-based immunity registries to businesses, several Miami hotels are reportedly rolling out an immunity app with their staff and guests next month and Delta Air Lines has expressed interest as well.