Warning - don't rely on UA agents for int'l COVID rules!
It should be obvious, but a UA customer care agent is NOT your best source for the COVID rules on entry to other countries. And can be dangerous to your travel plans.
Last night, I had a very nice agent who was convinced that I would have no problem as a US citizen entering ZRH from the ORD-ZRH Swissair nonstop (or any itinerary "originating" in the US). When I explained the current Swiss rules, she pulled up something on her computer from UA, read it thoroughly and still insisted I'd be fine on the nonstop.
As of now, that UA agent is completely wrong. US citizens will be allowed in if they have first cleared immigration in a "neighboring Schengen member state" or other low-risk country (which US is not, per CH immigration). But US citizens will not be admitted if they come nonstop from ORD, EWR, IAD etc. or transit through another country without going through immigration there. (There are exceptions but they don't cover the random tourist or granny trying to see her grandkids) CH Immigration still has US designated "high risk". Yes, once you are admitted by CH Immigration, a US citizen who is fully vaxxed doesn't have to pre-test or quarantine - but that's no comfort if you can't get past Immigration!
So don't rely on UA for your COVID planning, without checking a more official source.
SIGH.