Baby's first sickness...?

at what age was your baby sick for the first time? Was he fed or formula fed? At daycare or home? My DS just turned 4 month, is fed and cared for at home...now it seems he caught a cold.. runny nose and congested chest..I'm going to the pediatrician tomorrow and was just curious about how long can a baby go without getting sick.. I thought feeding would have kept him healthy for longer..