Andrew Niccol is back on to direct The Host. He pulled out of directing when it conflicted with his other film, Now. Apparently, things have changed. Susanna White was previously attached to direct when Niccol pulled out.
In the same article, it mentions that Saoirse Ronan will be Melanie Stryder, yet the interviews that have been posted to this site seem to suggest otherwise. It could have been locked down today. Who knows?
The film is being marketed and sold at the Cannes Film Festival which is going on right now in France.
Source: The Hollywood Reporter