This is the way I see it... We're getting boosters ahead of the period where people mix more and more indoors, plus now we have a new variant of concern. Having increased efficacy for December means we don't have to go out over Xmas and into the colder months, I also suspect volunteer numbers and people willing to go out in Christmas week is lower. Getting people out sooner and picking up people not having their first jab makes sense to me, plus there is probably issues with demand, spreading out vaccines across the UK and reducing wastage due to shelf-life. As far as I can tell no-one is forcing us to have a booster (yet), we are being offered and recommended one. So you can wait up to 6 months if you wish but if I was 50+ or immuno-compromised, I would be taking it as soon as offered. The government has been heavily criticized for failing to act quickly and not shutting down the borders fast enough (remember how the borders stayed in open during Kumbh Mela). I think this time they've responded appropriately.