If the question is whether vaccine should go to someone who hasn’t been vaccinated or used as a booster for someone who has, it seems clear that it should go to

If the question is whether vaccine should go to someone who hasn’t been vaccinated or used as a booster for someone who has, it seems clear that it should go to the unvaccinated person unless the booster candidate is very high risk. But we don’t have a shortage of vaccines in the developed world, only a shortage of smart people willing to take them. Bottom line, a booster shot reduces the chance of a variant emerging. You don’t want immunity to parts of the virus that aren’t the spike protein; that’s a waste of resources. The spike is what’s needed to reproduce.