The reason is just the natural way female and male bodies function and interact. 4% per year male to female; 03/01/2018 · according to studies done by valtrex, these are the rates of transmission per year of regular sex: I've only had one outbreak, as far as i know, and the only symptom that i can recall was an incredibly bad pain in my lower back, which my doctor seemed to think did not suggest herpes. Cold sores contain high concentrations of the virus and hence increase the chances of transmission significantly.