what does " fully one half " mean ?

[Peelee]

« Few diseases present greater difficulties in the way of diagnosis than malignant endocarditis, difficulties which in many cases are practically insurmountable. It is no disparagement to the many skilled physicians who have put their cases upon record to say that, in fully one-half the diagnosis was made post mortem. »

(William Osler, 1855)

what does fully one half mean? more than one half? no less than one half? just one half ?

One half, but in a scenario or situation where one half is a staggeringly bigger percent than it should be.