It depends, as MRex said on Belgian law. From my utterly non legal perspective that would focus on how it interprets section 6... if something happens we will all agree to sit down and discuss our options, we will not throw out threats of legal action.
We know there was a similar agreement with the UK as, when the same thing happened here, there was just a deep breath and, we need to wait attitude.
That in itself undermines the EU suggestion that the UK contract was inherently different.
Using Stella's own terminology, it wouldn't be fair to penalise the UK in order to allow EU output to skip the same teething issues. And that's before you look at what the teething issues actually were (or were not if you want to continue the EU paranoia that it was all a lie in the first place).
This is all short term thinking. In a month, probably less, the UK, Canada etc will be able to quantify their excess holdings. Note I am talking about countries in the depths of winter with huge numbers in hospital. They will be over that height and will be able to divert much higher amounts to countries not quite at the same pandemic point.
The EU should be doing the same but cannot as they were unlucky, bet on the wrong vaccine horse. As did many other countries.
That's the bottom line. Differences in vaccine procurement and the Commission's heated response.
It should blow over, but the ramifications could be interesting... in an uneasy way!1