We hear that extending the time between covid jabs gives better protection - lucky because I feel they lengthened it to get as many people 1 jab as possible.
It was also based on evidence for how other two part vaccines work and the optimum gap being longer rather than shorter.
The reason it was 4 weeks in the first place was simply because when they were trialling time was of the essence and they could get back results for a 4 week interval much quicker than a longer gap. They just didn't wait to see which was better in the rush for the vaccine.
The UK decided that the longer gap made sense because it meant we could partly vaccinate more people but also because there was a compelling scientific argument that it was more beneficial too. It was a gamble but an educated gamble.
It wasn't blind luck and a stab in the dark or rationing vaccines. It was a considered decision which seems to now be paying off.
The thing we didn't know at the time was how long vaccine effectiveness lasted. Thats the bit we've got lucky on in terms of timing.
But again its always been arguable that coming into winter there would need to be a top up in the most elderly because of what we know about the flu. Hence why the UK decided on a booster plan very early when there was only minimal data starting to come out of Israel. It was still very a very controversial decision at that point. I don't think it looks as controversial now...