Essentially the vampires would need to be extremely difficult to detect that they are present in modern society. There are three obvious routes to achieve this.
One, vampires may have a worldwide distribution, but they are extremely rare. For example, if only one in a million persons were vampires this will make them hard to find. Lower ratios will make vampires even harder to detect.
For example, in Jack Butler's novel Nightshade (1989) there is only one vampire and he lives on the planet Mars (the novel is set in the future).
Two, vampires only need very small amounts of blood to feed and survive. Presumably, this will mean they eat and drink other food for their primary sustenance and survival. So there will be no exsanguinated corpse to worry about or dispose of. Also, perhaps, no puncture marks in the neck too. The taking of blood might involve, for example, lapping the entry point of minor wounds.
If vampires needed to feed often, there would be an epidemic of people with puncture marks. If their victims were drained of blood, then it would be easy for legal enforcement to detect exsanguinating serial killers. Nothing says Vampire! more clearly than this.
Three, vampires are quite different from traditional supernatural vampires. No exclusively hanging around during the night. No fangs. No harm from sunlight.** No allergies to garlic. They may die like normal human beings from having a stake driven into the hearts. No crumbling into dust. In this case vampires could be given a medical examination and no-one would realize they were looking at a vampire.
On the other hand, if vampires are more widespread and less rare and are closer in function and behaviour to traditional supernatural vampires then there is one aspect of vampires that can explain their apparent non-existence in the modern world. This, of course, is the vampire's powers of mind control. Usually victims can be manipulated and controlled by vampires for easy feeding. What if those mind-control powers were much more powerful?
Now vampires could manipulate the minds of anyone who came in contact with them. Institutions and social organizations could be set up and controlled by vampires for the benefit of vampires. Perhaps, feeding stock could be organized on specialist farms. There could be covert blood banks where vampires could make withdrawals. Deposits could be arranged to be supplied by donor farms. Blood might even be diverted from legitimate blood banks.
This answer looks at two models of vampires to explain their non-visibility n the modern world. The first model considers vampires are rare, micro-heamophages and quite different from traditional vampires. The second model is based on traditional vampires but considers their cryptic*** nature is a consequence of powerful mind-control powers. This model included the creation of social institutions and organizations to support vampires and keep them hidden.
**: In Bram Stoker's Dracula the King Vampire himself could go about during the hours of daylight and was unaffected by sunlight. No sparkling or crumbling. Vampires crumbling into dust when exposed to sunlight was introduced in the German silent movie Nosferatu (1922).
***: "cryptic" in sense of being hidden.