From the BBC article on the vaccine decision.
"The CMOs concluded this tipped the balance, given the virus was going to keep spreading during winter.
They said this would continue to cause disruption to face-to-face education, given the policy in all parts of the UK of asking people who test positive to isolate for 10 days.
Earlier, Prof Chris Whitty, the lead CMO for the UK, said it was a "difficult decision" and should not be seen as a "silver bullet"."
So to summarise, no-one is seriously arguing that there is a health basis for vaccinating healthy 12-15 year olds as they are generally not seriously ill anyway (vulnerable 12-15s obviously different, and already offered to vaccine). Recent studies have warned that the risks of the vaccine are around 6 times higher for boys in this age group than getting COVID. On top of this it's estimated that a majority of this age group has had COVID anyway (most with no issues at all, may not have even noticed), and will therefore have some natural immunity anyway, making the marginal benefits of vaccination even less clear.
We know that the vaccine will not prevent COVID entirely, and there is no suggestion that children given the vaccine will be exempt from isolations etc. Additionally, Chris Whitty appears to be heading off any expectation that this will have a significant impact on spread. And yet, this is still the official recommendation, on the basis that COVID spread will cause disruption to education because the policy in all parts of the UK is to ask people who test positive to isolate for 10 days. Maybe instead of subjecting young people to risks that are not for their medical benefit (a fact conceded by all parties), we could stop using them as human shields and change the policy instead? Perhaps if we stopped routine asymptomatic testing, and only asked people who are ill to isolate for the duration of their illness instead of an arbitrary 10 days, the disruption to education could be kept to a minimum without all this. If indeed most teenagers have already had COVID, the chances of them being seriously ill with it again are really vanishingly small. Perhaps it's time to put children first.