It’s the zombie apocalypse. Coming at you in a dead run.

And I do mean dead. And I do mean … run!

Not — for producer-star Brad Pitt and director Marc Forster — the shambling undead of George Romero movies, or for that matter of the Max Brooks novel on which “World War Z” is very loosely based. No, the zombies in “World War Z” are speed demons, mindless yet displaying hive-mind swarming behavior as they pelt pell-mell over the landscape, bringing contagion and chaos with each and every snap of their ravening jaws. “Z’s” are truly insta-zombies. Full-blown zombification takes place mere seconds after a hapless victim is fatally chomped.

Forster (“Monster’s Ball,” “Quantum of Solace”) wastes little time plunging the picture into full-blown terror mode. After a tedious opening sequence in which it’s established that Pitt is a loving suburbanite family man, Forster plunks the family down in a traffic jam in downtown Philadelphia where everything is unremarkably ordinary … until it isn’t.

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Things go from zero to zombie in about three minutes flat with crowds suddenly fleeing in panic, cars crashing like crazy and explosions ripping through the City of Brotherly Love. Civic order disintegrates instantly, and Pitt puts pedal to metal to save his loved ones as zombies hurl themselves at his getaway vehicle.

The picture then jumps around the world from Philly to South Korea to Israel and elsewhere, locales where Pitt’s character, a former U.N. worker whose ill-defined job description has sent him to lots of global disaster zones in the past, survives ever-closer encounters with the brain-dead legions as he tries to determine what caused the zombie contagion and, furthermore, how to stop it.

“WWZ’s” addiction to speed is both its strength and its weakness. Its rapid-fire series of swarm-attack sequences (surprisingly bloodless) are jolting. But the movie moves so quickly that it offers few clues early on as to why the authorities consider Pitt’s character to be so vital to the effort to contain the plague. And it offers no clue at all as to how those authorities had time to set up a sophisticated offshore ship-based zombie-fighting command center that’s a key component of the plot.

However, given its troubled production history (lots of script rewrites and reshoots here), “World War Z” is certainly a genuine nail-biter. Chomp!

Soren Andersen: asoren7575@yahoo.com