It's not hard to believe at all if they've been kept magically hidden, either by their own means or beacuse the sorcerors (or somebody else) were keeping them under wraps somehow.
See, that's writing for people who never adequately addressed the lack of awareness of vampires in the modern world, and one would ask:
why would they be magically hidden--especially in a MCU world where its overpopulated with the super, the supernatural, alien and anything else that fell out of fantasy-themed tree?
Or if they were all killed off in the past but someone brought them back again as has happened in the comics. Or if they were just really small in number and under tightly controlled rules to not leave any trail of bodies behind them. Etc, etc.
Ahh, but the existence of Blade (how he came to be afflicted / spent his formative years) meant they had to have been operating in the world for some time--decades (if Blade will be in his 20s), so they were not hidden away. Anyone can attempt to write around that, but again, his existence means vampires were operating in the world, not hidden away, or recently resurrected.
It's an extremely simple thing to write around.
The comics were never very good at creating reasonable explanations for the general population not knowing about vampires when doctors, superheroes, John and Jane Q. Public, the police, et al., all had run-ins with Dracula (in
Tomb of Dracula) and his various groups of vampires. For some reason, writers wanted to take vampires out of the 19th century-styled isolation and drop them in the then-modern day, but were never prepared to address how that would look if set loose on the streets of places like the U.S.
Note: Joke.
