Hi,
Yes, unfortunately they can still get KC as there are a whole heap of strains out there (kind of like the human flu) and the vaccine only guards against 1 or 2? of the worst strains.
In case it is KC, make sure you do full barrier treatments and no sociallising them for several weeks.
The cough syrup should help.
The conjuctivitus would be a result of his immune system being run down. Wash eyes with salty water or tea also helps. At least 4 x daily. Also a good idea to give him vit C to help him out.
Hope your guy feels better soon.
Belnel