It's a bit weird for sure, since the cure was in place in school and seems to have been permanent.
Else radio person could have been sick and just staved it off with cures until cures ran out and they died - which would also have explained why they died so long after the outbreak, despite probably not having been out much since.
So maybe cure isn't permanent for all? It was supposed to be experimental. Or there's differences in effect depending on how you get infected. None of the previous cases seem like they would have been able to degrade into a state of not being able to write and yet manage to lock themselves in after that.