Not to mention the gallons of bloody vomit.

For those of you bad at math, “28 Weeks Later…” picks up the action six months after the first movie (I know 28 weeks = 7 months, but the first movie picked up a month after the outbreak). Actually that’s not entirely true; the opening scene takes place concurrently with events of the original. In it, a group of folks that includes married couple Don (Robert Carlyle) and Alice (Catherine McCormack) have barricaded themselves in a farmhouse, eating canned goods and doing their best not to attract the attention of the hordes of Rage-infected maniacs roaming the countryside. They fail, of course, and the ensuing attack claims Alice’s life, no thanks to Don’s rank cowardice. Then again, what better excuse to dump the starter wife than a zombie apocalypse? At any rate, Don barely escapes.

Fast forward six months. The Rage virus has apparently disappeared (Great Britain, we learn, was successfully quarantined), the reconstruction of London has begun, and the American military is in place to keep an eye on things as people slowly start repopulating the city. 50,000 civilians have thus far returned to the city’s Green Zone, situated on the Isle of Dogs in east London. Cleanup continues in the rest of the city, and travel outside the Green Zone is forbidden.

Two of the most recent émigrés are siblings Andy (Mackintosh Muggleton) and Tammy (Imogen Poots), the first children allowed back into the city, who are about to be reunited with their dad. Unsurprisingly, he turns out to be the hapless Don. Don is now some sort of a facilities supervisor, with access to all areas of the compound. As you can imagine, this will be of some importance later on.

Andy and Tammy, being kids in a horror movie and therefore unable to resist the machinations of the screenplay lure of a deserted city, sneak into London proper to goof around, thereby setting off a string of events that will culminate in a much-anticipated Rage-a-thon.

The first half of “28 Weeks Later…” is highly enjoyable, assuming you find things like cowardice, official incompetence, and nihilistic visions of the future entertaining. Director Juan Carlos Fresnadillo, who was essentially handpicked by now-executive producer Danny Boyle, gives us a more depressing look at humanity while retaining several of his predecessor’s moves. This isn’t always a good thing, since Fresnadillo can’t seem to get his fill of low-light hyper-edited fight scenes or frenetic hand-held shots of people running, but when used right it adds to the sense of claustrophobia and impending doom.

Once the action really starts (let’s just say the Army’s “containment strategy” isn’t quite as well-implemented as the one we used during the Cold War), we’re treated to what amounts to “Aliens” with insane cannibals instead of xenomorphs. You’ve even got the mother surrogate (Rose Byrne) and the sensitive soldier (Jeremy Renner) escorting the children to safety. And instead of squaring off with mama alien, they’re stalked at each turn by Daddy Zombie, for Don has become not just an Rage-infected psycho, but its very paragon, able to avoid precision napalm strikes and snipers and open locked doors, something beyond the abilities of his fellows.

There’s not much new to “28 Weeks Later…” We get lots of running and shooting and spewed blood. There’s one scene directly ripped off from “The Descent,” nerds will argue for decades over whether or not this movie came up with helicopter-vs-zombie before “Grindhouse,” and the ending pretty much eliminates the need to make “28 Months Later…,” but I enjoyed it. R-rated horror is always welcome, especially when it focuses more on dread and hopelessness than plucking out eyeballs.

Having said that, of the movies opening this weekend I’ll wager “Georgia Rule” is more terrifying.