...and that's the problem: the MCU (in-universe) is no longer at a point where the fantastic is rumor, a story or something written off as a hoax; they've experienced every type of superhero, supernatural (i.e., magical) being / creatures, aliens and everything in-between, and with that running around earth (with many posing direct, open threats to the population), vampires would no see no reason to conceal themselves in a world that become a free-for-all for threats to the human population.
If vampires in the MCU were going to work at all, the logical starting point would have been to seed the concept as far back as the still unpopulated field of the first Iron Man or The Incredible Hulk era, where its hinted at, but the "eye" (so to speak) of the MCU was not yet ready to visit / tell that story.
To a degree, vampires in the current MCU remind me of a line from the John Leslie Stevenson character (aka Jack the Ripper) in Nicholas Meyer's Time After Time:
"The world has caught up with me and surpassed me. Ninety years ago, I was a freak. Today, I am an amateur."
You'd have to assume the residents of the MCU have been shaken from their everyday sense of comfort to no longer be as shocked by the strange or otherworldly, which would allow "amateurs" such as long-"lived" vampires to exist among humans in a more direct fashion, but not seem like the all-out threat it tends to be in stories where the world is utterly devoid of all other supernatural creatures, so they would appear to be a greater terror.
Just because some supernatural phenomenon are public knowledge doesn't mean all of them have to be. In True Blood, when the show starts vampires had "come out of the coffin" as they put it in the show, years ago, but were, shapeshifter, faeries, ect. were all still secret.
And really it makes sense that vampires would want to continue to keep their existence secret, since they are stealth hunters, and it's a lot easier to lure in your prey if they don't know you exist. And there's also a pretty good chance if people do find out they exist, you're going to get a whole lot more people going after them, if humans are still their primary food source. The only reason they came out in True Blood was because once they invented artificial blood the vampires had easy access to an alternative food source.
The vampires Frost confronted were in the open, and once he turned, he too was not hidden away (the reason he could pose as a doctor to gain access to Blade's mother).
OK. I just read through Blade's origin on the Marvel Wiki, and the whole vampire doctor feeds on his pregnant mother, and makes him a dhampir would work just as well if vampires weren't common knowledge. The only difference is that would be a doctor who was secretly a vampire, and he would have to attack Blade's mother in secret.
