First off this is the link to MIT.
Will you have to carry a vaccine passport on your phone? | MIT Technology Review
There's a lot more to the article but here is the point you should be aware of. Immunization doesn’t mean safety
While several vaccines appear highly effective at preventing symptoms of covid-19, we don’t know whether they stop people from catching and spreading the virus asymptomatically. Trials of the Oxford-AstraZeneca vaccine suggested it may limit transmission from asymptomatic carriers, but Pfizer and Moderna’s trials didn’t regularly test participants for the virus if they didn’t have symptoms.
More data is needed to prove conclusively that vaccination prevents you from giving covid-19 to other people, and how long immunity lasts. It’s also important to remember that what’s true for one vaccine may not be true for another.
Without these crucial pieces of information, vaccination credentials only prove that you received a vaccine on a particular date—not that you do not have and cannot catch the disease. In the meantime, a negative covid test remains the best evidence that you’re not contagious. And since tests are far from perfect, you should still follow public health guidance about limiting spread whenever you can.