It depends on the infection, if you get TB or any other mycobacterial infection you will be taken off, but most infections don't form a significant threat to warrant stopping a biologic.
As far as skipping a dose, that's usually avoided if it's not needed because your body will start to produce antibodies and memory B cells which can cause an adverse reaction.
I only went on biologics (infliximab) long ago for a few months, but I can never go on them again because I developed antibodies, my body will reject it.