Everyone is making decision under uncertainty, all the time.
If my impression of risk-loving decision making is wrong and there really was careful analysis of risks I'd love to hear it. It would restore a /lot/ of faith.
What was the assessed risk that that an increased period between first and second jabs would greatly reduce the coverage?
What was the advantage of the increased period? (ie is it likely that one jab will keep more people alive and/or do less damage to more covid survivors).
Is the risk of going with a longer period between first and second worth it? With the benefit of hindsight there appears not to be a downside. To be totally clear: this is very, very, very welcome news. Now it's a proper asymmetry and it seems like this strategy is all upside from here.
The alternative was to give people the two vaccine jabs the exact amount of time apart as had been tested and was known until this data came in. Then switch to this strategy. That is the conservative decision as you pretty much know what you're going to get. Is the longer period between first and second to get more people a first jab faster going to pay off? Again to be 100% clear let's hope so. Really let's hope it's a huge, huge win.
This analysis of UK vaccination policy and the maximum coverage of first jabs that the new 3-month data helps to further (but not completely) inform has nothing to do with the EU or New Zealand or Taiwan or Brazil.
Assessing the UK's gamblers' strategy of taking flyers is a reasonable thing to do in comparison to other EU nations, or NZ or Brazil...
There are other aspects to the UK's various strategies that don't have much to do with the Oxford vaccine showing sustained protection of 76% ...
If the UK has made some good calls in there based on risk asymmetry and balances of probabilities to go with the plethora of terrible ones they probably should trumpet them very loudly just restore people's faith that it's possible and that we can do better than 'gut-feel' or taking a flyer or "if she comes home we'll be loaded!" Which is how it's looking.