When I went to donate my pint of O positive tonight, the staff told me about the recent cyber attack that meant London hospitals were unable to process a lot of their stock of blood, meaning that loads of it went out of date and had to be disposed of.
They especially need O negative, which can go to anyone, and O positive, which is safe for anyone with a positive blood type.
The other thing I learned is that each blood donation can help to save three people.