The applicant pool is plenty well stocked, so there is no "shortage" of teachers. What there is, perhaps, is a shortage of qualified teachers in the classroom. In other words, due to budget cuts, layoffs and position cuts (i.e., not hiring a replacement after someone retires or quits), there are not enough employed teachers to adequately teach all the students in the states with a so-called shortage.
But there are plenty of qualified people looking for teaching jobs -- more than enough for current openings and then some. So what this is, is a money problem. There's no teacher shortage, there's a budget shortage. We're not allocating enough funds to adequately fill needs in schools across the country.
Or at least, that's how I see it.