@Gordon0 Yes - thanks for this info. I had a lot of sympathy though having discovered it is near impossible to get travel insurance and the restrictions on getting back into, in this case, Switzerland are severe.
My personal belief is that Airbnb should now change the rules to allow guests to cancel if their trip becomes untenable. Without this and with travel insurance hard to find I believe guests will just not travel. Clearly Airbnb should not change the rules retrospectively.
I suspect a lot of hosts will be faced with decisions over the coming weeks as I see the USA is considering a 7 day quarantine for arriving travellers.