More and more places are starting to require vaccines for work, school or to get into concerts, bars and restaurants. That means we’re going to need a way to prove vaccination. There’s the paper card from the CDC everyone gets with their shots, but also digital vaccine passport apps. Marketplace’s Meghan McCarty Carino speaks with Laurin Weissinger, who co-wrote a paper for the  Brookings Institution about vaccine verification systems. Weissinger says we’re starting to see these apps pop up in the U.S., but there’s a lot of variation.