I’ve arranged travel for several clients who went for the express purpose of vaccination.
If you’re related to an Argentine you can fly no problem even if not a PR*. (With one important caveat - see below). If you’re a PR you can fly, case closed.
*The only issue with traveling as a relative is that the relationship must be documented in a manner acceptable to Argentine authorities. If you married an Argentine in Argentina, you’re home. Same if you had a child born here.
But if, say, you married an Argentine abroad, or you are Argentine but have kids born abroad, the marriage certificate, birth certificate and whatnot must be apostilled, or legalized by an Argentine consulate. Otherwise, the document has no value here.