Vaccine neutralises Omicron with three shots

Anyone have an idea why on why a variant would require more doses to protect?

Is the implication also that you'd be better protected from the alpha variant too, just that you enter diminishing returns for the third shot there whereas for variants diminishing returns don't kick in until later shots?

from what i've heard the symptoms of omicron aren't very severe anyway. couple of recent videos from the last day or so are pretty encouraging https://youtu.be/BtELl7-zE_w https://youtu.be/5E6gpPJwYIY