Insane idea. Beyond the OBVIOUS myriad constitutional violations, the administrative nightmares its implementation and execution would entail (a few issues might include: who/what agency would enforce it, budget for enforcement, who would adjudicate it, the "little matter" of it not being FDA-approved, what to do about forgotten paperwork, hassles of checking paperwork of every member of every family during holidays when airports are already swamped, definition of "immunized" [is it immediate like for concerts/restaurants or after the 14 days per the government's own definition], unequal treatment of exempt persons [illegal aliens, exempt federal employees, etc.] versus non-exempt on the same flights, immunizations "expiring" before final/return leg, "expired" immunizations, children having birthdays that put them into categories requiring the jab before a return leg/trip, etc., etc., etc.) make it one of the most boneheaded, ill-conceived, virtue-signaling proposals put forth in some time (and THAT is saying A LOT, given other clown-world legislation that has been proposed in the past couple years).