Viruses are no different from bacterial infections as far as immunity.
I was on Imuran as well as Humira and I never got sick, even after being around people who were. Maybe I was just lucky.
Keep hand sanitizer with you at all times. Remember not to touch your face as well, and get lots of rest!
I'm on Remicade infusions and I was told that I was not supposed to use biologics when sick. You might want to talk to your gasto.