It is a fragment of an antibody. I'm guessing the took a neutralizing antibody and started trimming it down to the minimum needed. Smaller could be easier to make but it is also patentable if it is not found in nature. Hard to patent an unmodified antibody since it would occur in nature.
Anyway, the paper was slow to load so I haven't read it yet, but it could take a while to get the studies to show it works and is safe. Most of the things we have tried so far have been drugs where safety was already known.