Well, the Clalit preprint relying on more data by an order of magnitude will be out soon, and that should be the definitive analysis.
However, current results for a Pfizer 1st-only regiment aren't very encouraging IMHO. It's possible the first dose starts to be really effective exactly at the time Pfizer suggested to have the second dose, and that this increase is rather sharp - But it would be some coincidence, and antibody tests (showing not so good efficiency against variants following 1st dose, and also much larger antibody count after 2nd dose) are contraindicative.
Didn’t Israel test antibody levels post-1st dose, and come out with results that it’s around 50% by week 2 and 90% by week 3, before taking the second shot?
If I’m not mistaken the claims that the levels are low (and efficacy only 50%) were because some sources took average of days 1-21 instead of 14-21.
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.
True, but I am not sure that changes things. It's possible that the dose increase doesn't lead to a relevant clinical difference.
Ultimately, someone will have to do real world analysis and get conclusions from that. Right now, IMHO, there's better reason to think that a smaller Moderna dose is fine than to trust a single shot Moderna vaccine regiment.
However, current results for a Pfizer 1st-only regiment aren't very encouraging IMHO. It's possible the first dose starts to be really effective exactly at the time Pfizer suggested to have the second dose, and that this increase is rather sharp - But it would be some coincidence, and antibody tests (showing not so good efficiency against variants following 1st dose, and also much larger antibody count after 2nd dose) are contraindicative.