I'm not sure what your 50% and 90% refer to. 50,90 percent of what? There were tests showing an order of magnitude more antibodies a week following 2nd shot (e.g. [0]).

The efficacy claims were because disease levels took more time to drop off than what one would expect following lockdown+start date of 1st shot vaccination if 1st shot were effective. I lack the qualifications to evaluate these claims, but I can tell you all Israeli HMOs prefer the 2 shots regimen.

[0] https://twitter.com/ArielMunitz/status/1356683799568990216