however, practically nobody cares. I have traveled to the US more than 10 times in the last three months, no one ever asked my proof of vaccination, I once even challenged the customs officer and insisted on showing my proof, guess what? he ignored me. It is possible the airline staff may ask for your proof when you check in through the counter, I usually check in via KIOSK and have no check in luggage, thus never interacting with an airline staff.