Again the EU wants to take on the UK, but who is correct for you can’t expect any contract to not be respected.
The UK contract is with AstraZeneca and not the EU, and we are not responsible for any assumed noncompliance with a contract which has nothing to do with the UK.
Should the EU retaliate by putting a trade block on Pfizer BioNTech exporting their vaccine to the UK, then the UK could retaliate by putting a Trade block on Oxford/AstraZeneca exporting their vaccine to the EU.
Both would be against international trading rules, but who went first.
Should the EU be so vindictive, then who would trust the EU ever again.
To mitigate any problems the UK should immediately stop using the Pfizer BioNTech for first vaccines and recommence using for second vaccines, then use Oxford/AstraZeneca for first and second vaccines and so on in Spring 2021 for the Modena vaccine.
Yes, it is childish and 2 wrongs do not make a right, but if the EU want to be childish then what should be done, well the EU should act responsively as they stated they wanted the UK to do when we threatened to break International Law when we were negotiating the Brexit Trade Agreement.