Five seasons in and “The Walking Dead” shows no signs of slowing down. If anything, it’s the opposite. About 17.3 million people watched the Season 5 premiere Sunday night, the highest ratings in the show’s history — and an absurdly large number of viewers for a cable drama.

Somehow, the zombie drama turned out to be a perfect storm of everything a cable network needs for a huge franchise: A plot that stretches along eternally, without the convoluted twists and turns that demand closure on other hit shows. An interchangeable cast that suffers little if a key person is killed off. Massive ratings despite no awards show recognition. Lots and lots of zombies.

And it’s worked: “The Walking Dead” is still routinely among worldwide trending topics on Sunday nights, in addition to its millions of viewers. “Talking Dead,” the weekly after-show devoted to analyzing the drama that preceded it in talk-show fashion (no, seriously) can land around 5 million viewers, numbers that certain broadcast networks would kill to have for their own dramas.

Naturally, plans for a spin-off are moving right along. In the announcement of the pilot order, AMC President Charlie Collier joked that the most frequent question he gets — besides fans asking whether they can make a zombie cameo — is about how the zombie apocalypse is playing out in the greater world beyond its Georgia setting. Seems like that will be the agenda for the new show. The network is casting for a bunch of new characters.

Meanwhile, unlike many other serial action thrillers — we’re thinking of the meandering “Lost” and “Homeland” — “The Walking Dead” doesn’t bog down or burn out in a mystery that must be solved. What caused the zombie epidemic? Who cares: Writers quickly established a journey for day-to-day survival as the entire storyline rather than a climactic save-the-world plot. And viewers seem to be satisfied with a plot that continues to mull the ethics of human behavior at the collapse of civilization — not to mention the many ways to kill a zombie.

“Walking Dead’s” willingness to send key characters to their grisly ends is actually a win-win. The show simply adds new characters, the audience stays loyal, and some dearly departed regulars go on to better things in showbiz. As the Hollywood Reporter points out in a story about why “The Walking Dead” stars have trouble landing bigger roles on film and TV, the actors fare better once a character is killed off, such as Sarah Wayne Callies (Lori) and Jon Bernthal (Shane), who both have new TV shows and movies lined up.

Through it all, producers seem to have moved beyond even caring about award shows. The show has won two Emmy Awards for prosthetic make-up category, and a few nominations for sound editing and special effects — the Golden Globes gave it a Best Drama Series nod back in its first season. Since then? Zilch. But with 16 million viewers tuning in in any given week, it’s highly unlikely that the network executives are losing sleep.

Speaking of the network, coincidentally — or maybe not — the highly-rated Season 5 premiere comes right on the heels of the announcement that AMC will halt production on all unscripted shows, aside from “Talking Dead” and a few others. “Scripted originals are at the core of the AMC brand,” the network said in a statement, citing “Walking Dead,” “Breaking Bad” and “Mad Men.”

Except that “Breaking Bad” is long-gone and “Mad Men” will wind up next year. So if the spin-off works out, the “Walking Dead” franchise (already renewed for a sixth season) could make up quite a bit of AMC’s original programming. But something tells us the network won’t mind that one bit.