By my estimate there are only 4 left at this point, I think we all assume they'll be killed when The Governor launches his assault on the prison, but honestly I was hopin there'd be a couple more around for the slaughter.
Heres the math maybe I'm off by 1 or 2: Greg Nicotero confirmed on Talking Dead that there were roughly 45 people in the prison at the start of the season. Now we take out the 14 real characters (Rick, Carl, Glenn, Daryl, Carol, Hershel, Maggie, Beth, Michonne, Tyreese, Bob, Sasha, Lizzie and Mika) plus Judith, that leaves us with about 30 redshirts. Zack and Patrick died in the premiere, 13 more died next episode (not including zombie patrick) 2 in Isolation, and now another 9 in Internment. 30-2-13-2-9=4
That said, I'm glad we're almost rid of these useless wastes of time, and I applause Scott Gimple and his writing team for working quickly to get rid of Mazarra's final 'fuck you' to TWD.