I am considering this issue now... and have been for about a week or so. I have plans to arrive in Spain Jan 1, 2022... with a walk on the Camino de Madrid...
A positive test requires 10 days of isolated quarantine, and that is what I would have to do: find a location ASAP that I could get to.
And that's a problem that might cancel all my plans because: there can be emergency acute flare-ups at home for a beloved with a chronic health concern. If I were to test positive at the point of an attempt t o return for an emergency... well that would be an unacceptable delay... which translates to: my entire sabbatical plans are an unacceptable risk.
Therefore, at this point, I am expecting to eat the cost of my flight and simply not go. I have not yet made any accommodation commitments, so it's only a loss of plans as far as that goes.
BUT: will the WHO, CDC, and EU Health Organization, PHAC and so forth have transitioned by January to: There will never be "COVID 0", the point of vaccination was to allow for people to be exposed to and even acquire the virus without becoming ill, and we must, therefore, permit people to live without mobility restrictions. Those who refuse to be vaccinated will not be permitted, I think, by 2022 sometime, to dictate whether others can live with freedom of movement. It will be the vaccine refusers who will have to stay put. The vaccine passports are already arriving in some Canadian provinces to allow people who are fully vaccinated to go to events, travel etc. Those who refuse vaccination are going to be prevented from exposing themselves to live virus in vaccinated communities. That is the only rational way to handle things from a policy perspective. One cannot punish those who act responsibly.
All that said, rules being what they are.... if I had not at-home considerations, I would simply go to wherever I was told to go, ASAP. My personal circumstances being what they are, Spain 2022 is completely in the air and subject to cancelation at this time.