I suggested 50% as more of an upper bound.

My current guess is I would be very surprised if these have very high efficacy, based on a number of studies on kind of similar vaccines I remember reading. I think the most likely outcome is that these have 0% efficacy, though I also wouldn't put less than 10% probability on them having between 20% and 50%.

But yeah, these are all just random guesses. Probably some biologists have better models here that could allow them to make better predictions, but there is no hard data.