If the doctor has an open herpes sore, there is something like an 90+% chance that he will transmit it to the baby.
Ok, but the directly relevant question is: What percentage of metzitza b’peh occurrences leads to Herpes transmission, versus what percentage of babies develop herpes anyway?
Let’s keep in mind, that herpes is hardly a rare virus. In one study I found on google, they found herpes virus in 98% of healthy participants. (herpes simplex virus type I (HSV-1)). So it is probably pretty normal for babies to have, but if I could be wrong on that conclusion.