Fungle infection, require advice

I came back from holiday on the 19th of July to find my 30cm asagi koi
had an infected sore in it's side near the tail. on the 23rd the sore
was cleaned, swabed with iodine and given anti-biotic injection. Fish
has been treated with idodine again on 26th, 29th, 2th August and today
(7th).

The fish seems no better and no worse. The water temperature is between
15 and 19 degrees. What should I do. I am worried about the other fish
been infected