Effectiveness was measured 2 weeks post second jab but was already high at 1 week.The effect on hospitalisations should be incremental as more of the most vulnerable get their second jab.
They need to be incrementally moving towards relaxing the most onerous restrictions as this takes place, and supporting the most vulnerable to avoid contact with others whilst they wait. Locking down everyone for as long as possible should not be the default option.
Supplies of the Pfizer jab are quite limited in the near term as the new manufacturing facilities are slightly delayed in coming on line hence with the Pfizer vaccine alone those increments will be very small over the next few months hence the CMO comments. Unfortunately politicians got a bit blindly optimistic about vaccines and the speed of impact. With current Pfizer vaccine availability they can only vaccinate around 20% of their phase 1 priority groups (groups 1-9)
If supplies are initially limited and vaccine logistics are difficult, the best option for case reduction in 4+ months comes from increasing the gap between the minimum three weeks to 4 weeks but they have been very silent on this so far, which suggests they are thinking about it.
The Oxford-AZ vaccine getting approved would be the big game changer in terms of roll out speed and number of vaccinations overall and hence be the driver of restriction reductions.
Given that the government has got burnt by relaxations a few times they will probably want to see the numbers falling first before relaxing and also relax incrementally.