There isn't an easy answer. Condom's reduce the risk of HSV by about 30-40% (if I recall correctly).
I'm curious about these stats, as they always mention if someone is not having an outbreak. What if they were having an outbreak (obviously you didn't notice) and you wore a condom? What would the stats be then? Anyone know?
I believe you can find on the expert's forum (STD) it being quoted as about 1 in 1000 chance from a one-time encounter. It's considered a low risk.
Aside from that, here are statistics that might be helpful to you, and put it into perspective of why the odds are low:
Here are odds based on female to male transmission of genital herpes.
FEMALE TO MALE RATE OF TRANSMISSION (HSV2 ONLY STATS IS NOT APPLICABLE FOR HSV1)
If you have 100 couples where the female has HSV2 but not the male (these figures are over a year) the odds of female to male transmission are, if you do nothing other than avoid sex during an outbreak, 4 men out of a 100 will get herpes in a year, or 4%. If you do go on a suppressive therapy then it drops to 2 men out of a 100 in a year, or 2%. And if you use suppressive and a condom the chances are 1 man out of a 100 will get herpes in one year or 1%.
The Valtrex and transmission study stats are based on having sex 2 times/week.
Are you taking any antivirials?
If not:
HSV 2 genital 15-20% of days evaluated
If you are taking antivirial's this lowers the days in which you will asymptomatic shed.