My understanding is that the spike protein already mutated in the human population, some time in January or early February. Researchers who started work on earlier samples had to start over because the later spike protein version has such superior fitness that it has largely replaced the earlier version in the wild.

So, stability over e.g. a month doesn't guarantee stability over longer terms.

Phase 3 is normally where most medicines fail.

Covid (any vaccine based treatment really) is even more difficult as you need to wait for six months to assess transmission.

> Covid (any vaccine based treatment really) is even more difficult as you need to wait for six months to assess transmission.

Technically, you don't. There are volunteers ready to get infected with SARS-CoV2 and I wouldn't put my money on "ethics" standing in the way in this case.

That is true, but you still need a relatively long time to make sure there aren't any nasty side-effects.