Promising stuff re a booster shot, but Not sure that the right conclusion to draw is that it should have been a 3 dose vaccine.
The initial 2 shot study results showed 95% (ish) efficacy when compared to unvaccinated, so is it possible that this 3 dose study is just indicative of the reduced efficacy of 2 shots over time (says the median was 11 months after 2nd shot), and the 3rd shot could also wane in a similar manner?