One vaccine by this August maybe. You do need two to have it done properly, and that's 3 months on + likely a few weeks post that to reach full protection.
So everyone who gets their first vaccination by the end of April - as things stand that's not going to be far off most of the vulnerable groups and the vaccines do appear to offer genuinely excellent protection against ending up in hospital.
It must be a very annoying decision as August might actually be entirely possible but impossible to be sure. I could definitely imagine it being possible to hold it in Sept/October, but I presume the logistics simply don't work for that.