Leading airline and business groups are asking the Biden administration to develop temporary credentials that would let travelers show they have been tested and vaccinated for COVID-19, a step that the airline industry believes will help revive travel. Various groups and countries are working on developing so-called vaccine passports aimed at allowing more travel. But airlines fear that a smattering of regional credentials will cause confusion and none will be widely accepted. “It is crucial to establish uniform guidance” and “the U.S. must be a leader in this development,” more than two dozen groups said in a letter Monday to...