marsha I think even at this most unreasonable, Pjizer will be able to supply the second dose for people that have already had the first.
The UK have more or less switched entirely to AZ now, so it should not be too difficult to secure the last batches needed to complete the PJizer roll out. Of course this is extremely damaging for Pjizer as well, who must be extremely adverse to not being able to supply the second doses for 90 years old grannies, and therefore putting their lives at risk!
So I think that is unlikely even in the current climate.
In terms of delays here, we do have production here and we are steaming through through the numbers. A small delay is possible, but we have many other vaccines coming on board, so I am personally not worried about a big delay to the roll out.
It would be better if the EU were vaccinating properly in the same way we are, to better protect the continent from mutations, but this was always going to be such a tall order given the sheer population numbers - hence the travel restrictions. EU likes to think it is on par with the US, but they could never hope to vaccinate 100 million in 90 days they simply do not have the infrastructure.