It is however not that strange. O Negative is fairly rare. Only 8% of Caucasians have it, 4% of the Latino and African American community, and even only 1% of the Asian community. Taking into account that it is an universal donor, it is often used if there is no time to type match. So it is a limited group of people that can give it, but it can be given to just about everyone. The American Association of Blood Banks just warned about the shortage of O Negative last year because it is overused.
Let's just see:
Literally the first five Google hits for O Negative Short Supply are within the last year, from five different periods, sources and areas.
What does short supply mean in this context? I'm assuming hospitals aren't in short supply of blood the same way Chipotle is in short supply of carnitas. Like what's the threshold? I have to imagine hospitals are prepared to go for a month or more on blood and meds, never actually running out completely.