Yes, they’re eggs full of blood. Well, not precisely blood; the xeno-species that lays Blood Eggs is compatible with our ecosystem, but it only vaguely has the same kind of DNA as do terrestrial species. Left alone, a fertilized Blood Egg will produce a ‘chick’ as usual; but unfertilized Blood Eggs produce instead a gloopy red fluid that smells and tastes like human blood, but can be cooked the same way that chicken eggs can. It’s absolutely unsuitable for transfusions, though.
On the other hand, it’s a perfectly good nutritional substitute for anything that lives on human blood, for everything from atomic mutant giant ticks to straight-up vampires (and the vampire thing, honestly, is what most people will care about). About three Blood Eggs will serve as a ‘meal’ for your standard vampire, whether fresh or cooked, and eating them will keep any cravings at bay for all but the most literally diabolic sort of nosferatu. Vampires also find that dishes made with Blood Eggs in them are much easier to ‘digest.’
In short, the introduction of Blood Eggs into a society with vampires is typically an excellent way to justify vampirism being a public condition. Vampires eat their Blood Eggs, and humans don’t stake them; everybody’s more or less happy with the results and nobody has to start a genocidal war. The humans can even tactfully ignore all of the blood-drinking which is just more or less just a particularly weird sex thing, and the vampires that aren’t actually into the weird sex thing can stop cultivating Blood Dolls or whatever the current slang term is. Things work out.
Well, as long as nothing happens to the Blood Egg supply. It’s probably safe to assume that there are people (both human and vampiric) who are dedicated to the task of making sure that nothing happens to the Blood Egg supply, but then it’s also safe to assume that there are other people (both human and vampiric) who are dedicated to thwarting the efforts of the first group. Admittedly, the second group typically is made up of crazy people of various stripes; alas, that just makes them a bit harder to thwart.
Fortunately, there are usually teams of specialists out there that do nothing all day besides thwart crazy lunatic schemers.