The good news is that US minorities are very unenthusiastic about getting vaccinated. Especially blacks. It’s mostly affluent whites who are most enthusiastic. The difference seems to be at least 15%/20%. So under US Civil Right laws any attempt at a COVID Passport will be found to be discriminatory and “racist”. Under California law anyone can file a Civil Rights complaint which must be acted upon even if they are not the “victim” of the “discrimination”.
So that idea is a complete non-starter.
But the State Dept has just introduced mandatory COVID test for legal entry. Unless you are an illegal immigrant of course. In which case its simple catch and release. No tests. At least 35K already in the pipeline with another 100K plus expected soon. The news out of Central America and the southern states in Mexico is that many hundreds of thousands are getting ready to head to the Rio Grand.