On Thursday, The CW’s “The Vampire Diaries” will mark its 100th episode a day before NBC’s “Dracula” airs its first season finale Friday at 10 p.m.

Both come more than five years after the release of the first “Twilight” movie and the vampire craze it unleashed on pop culture, helping popularize TV series like HBO’s “True Blood” and “Vampire Diaries.”

But as both those series have declined in viewership in recent seasons and with “Dracula” posting only so-so ratings in its 10-episode limited run — is there bite left in the genre?

“It’s got very wide appeal, especially among the youth,” notes Brad Adgate, senior VP/director of research at Horizon Media. “It’s also a very dual audience — doesn’t have specific appeal to either gender. That’s why it’s been popular. I don’t think that it’s done.”

“Vampire Diaries” executive producer Caroline Dries in fact credits the genre with helping keep the drama going for five seasons.

“The fact that we can be so heightened plot-wise allows us to keep stories feeling new and interesting,” she tells The Post from the show’s Atlanta set. “The intrigue of vampires, I don’t feel like that’s ever going to go away, it’s been around forever in literature. It’s that romanticized darkness about it that seems to be universal.”

“True Blood” peaked in its third and fourth seasons (2010-11), with its most recent season finale drawing 4.1 million viewers, the fewest for a finale since its first season. It seventh season this summer will be its last.

“Vampire Diaries” has declined since it premiered to a record 4.9 million viewers in 2009, the largest audience for a CW series ever. But its current season is still averaging 3.8 million viewers, including DVR usage, making it and its new spinoff “The Originals” (3.3 million viewers) two of the network’s most-watched shows.

“Dracula” meanwhile is averaging 4.7 million viewers on Friday nights — not gangbusters, but perhaps well enough for a genre that also sells well internationally. While “Dracula” producers have a second and a third season in mind, NBC has yet to pull the trigger.

“It’s tapped out. It runs in cycles,” says Daniel Knauf, executive producer of “Dracula,” of the genre. “After a while, people move on. It will be back in six or seven years. I think the whole vampire thing has been done every which way.”

The key with vampires, as with any genre, is to have a point of differention, with Dries pointing to the central love triangle between Elena (Nina Dobrev), Damon (Ian Somerhalder) and Stefan (Paul Wesley).

“If we can just keep the characters interesting and not lead into the supernatural elements of the show… then we can keep people’s interest,” she says. “The second it just becomes a vampire show people will get bored, because what hasn’t been done already?”

That won’t keep others from trying. FX is also looking to the vampire genre for its next high-profile drama with “The Strain” from filmmaker Guillermo del Toro. The thriller stars Corey Stoll (“House of Cards”) as the head of a Centers for Disease Control team in New York City investigating a mysterious viral outbreak of an ancient strain of vampirism — far from the romantic creatures that inhabit “True Blood” and the CW dramas.

“These are not sparkly, brooding dudes with fangs and romantic problems. These vampires, or to use the Romanian word, “strigoi,” are really scary creatures, and this is a really original re-imagining of vampire lore,” executive producer Carlton Cuse (“Lost”) recently told reporters at a press conference. “It’s a very layered force of antagonism that our characters are up against in this story, which I think also differentiates it from other shows in the genre.”