I wish we'd been told more about the nature of this trip.
Am I the only person reading this thread that had eyebrows raised at the idea of an 11 y.o. going overseas for a month without parents, let alone now being sick? I think, from the perspective of concern for others, putting that child on a plane and then exposing an entire group of children (in a part of the world where this virus may not be common) is unconscionable.
And that's on both the part of the parent AND the organizers of this trip (whatever it may be). In my mind they're actually worse because they have all the information they need to prohibit the kid from participating and it seems their only concern is CYB?