In groups under study, avoiding intimacy during outbreaks, somewhere
between 4% and 10%.

For the individuals who got it, somewhere around 100%.

Here's the old links and blurbs I haven't posted for a few months.
I haven't checked the links to see if they still work.

http://members.aol.com/herpesite/trans.html#risk
Risk of Transmission
In studies of transmission of genital Herpes in couples, the annual
risk of transmission averaged 5 to 10% per year for those abstaining
from sex during outbreaks. The risk of acquisition was much higher
(16.9%) for women, but somewhat lower for those who already had
HSV-1. There is some evidence that people who have HSV-1 are more
resistant to the HSV-2. This should not be interpreted as immunity
but rather as a higher resistance factor. The transmission rate was
also lower for those who used condoms.

http://www.obgyn.net/english/pubs/features/tfp/solomon_smith.htm
The risk of acquiring HSV-2 among sexual partners was prospectively
analyzed in a study by Bryson et al.(8)   After 16 months of
observation, 14% of initially HSV-2 sero- negative partners
seroconverted. All seroconverters were women, suggesting that women
are at greater risk for acquiring HSV than are men. None of the
couples in which seroconversion occurred used condoms or spermicides
during asymptomatic periods. There was an annual 10% acquisition
rate of HSV-2 among couples.(8)

http://www.viridae.com/gen4.htm?
In a study performed at the Universities of Washington and New
Mexico, heterosexual monogamous patients with genital herpes and
their susceptible partners were counselled on avoiding transmission
through limiting sexual contact to asymptomatic periods. This study
was on selected partners where one partner was known to have type 2
herpes and the other was known to be susceptible by means of a
type-specific blood test (Western blot). Transmission took place in
14 of 144 susceptible partners (9.7%). In most cases, transmission
apparently took place when the infected partner was asymptomatic. In
some cases, transmission took place during the prodrome or
pre-symptomatic period. Where the gender of the susceptible partner
was male (the woman had herpes), transmission took place, despite
avoiding active phases of infection, with an annual rate of 4.5%.
Where the gender of the susceptible partner was female (the man had
herpes), transmission took place, despite avoiding active phases of
infection, with an annual rate of 18.9%. This study also confirmed
that people with pre-existing immunity to type 1 herpes (eg, by
being exposed to cold sores earlier in life) were partially (but not
completely) resistant to subsequent type 2 genital herpes. It is
clearly wise to consider the possibility that asymptomatic shedding
might occur when making personal choices about preventing herpes
transmission. In case asymptomatic shedding does occur, properly
used condoms (safer sex procedures) are the best protection against
transmission and will minimize the low everyday risk that
asymptomatic shedding might lead to asymptomatic transmission. Using
sensitive and strict criteria for identifying people acquiring
herpes, this study showed that avoiding sexual contact during the
active phases of infection provides protection for more than 95% of
susceptible men per year and more than 81% of susceptible women per
year. It clearly showed, however, that simple avoidance of active
phases, alone, was not sufficient to prevent transmission. To
further minimize the risk of transmission to a susceptible partner,
safer sex precautions during asymptomatic periods should be used.

I can do better Bran.. here's a link that talks about HSV-1 and HSV-2:
http://www.yoshi2me.com/hsv1-hsv2.html

Merry CHRISTmas!!

Angela :)