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Erlkönig: HSV-2 + Suppression Risk Overview

It's pretty darn low.
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Researched for a woman whose sex partner (a cad) of some four times finally told her he had herpes, and was on suppression.

Some of the sources are missing, and there is NO guarantee about the statistics and statements below. You're on your own.


The risk of catching herpes (genital/HSV-2) is much lower from someone on herpes suppression than from some random person who just doesn't think s/he has it.

Herpes (genital/HSV-2) is NOT easy to transmit while dormant, and suppression keeps it dormant. Transmission of herpes generally occurs during outbreaks and shedding, when the virus is active.

For a scenario of a sexual fling, someone on suppression has a much lower per-sex-act chance of transmitting herpes than would a partner chosen randomly from persons claiming they don't have herpes.

For longer relationships, the relatively low per-act risk from one on suppression mean the risk builds very slowly. Obviously, the randomly chosen person may not have any cumulative risk, but the other people in that group are much more likely to transmit their infection, making the average risk of that group poor.

Things To Know

Herpes is transmitted skin-to-skin, not by male/female fluids.

And a lot of times it's skin in the pubic area, not the parts the condom would be covering.

Ejaculate (and preseminal fluid) isn't a significant risk.

Slather away; fluid isn't generally a way to catch herpes; it's a skin thing.

Herpes suppression therapy is about as effective as the Pill (in preventing what each is supposed to)
Chance of impregnation or herpes transmission based on sex frequency, with the Pill and herpes suppression in use.
Sex Frequency Chance per YEAR Of This Effect Notes
typical 9% Impregnated 9% is normal, but 0.3% for perfect use, q.v.
thrice weekly 7% Transmitted 7 ±2% (5 to 9%)
once weekly 2.5% Transmitted 2.5% ±0.5% (2 to 3%)

Perfect use of the pill means: same time of day, no mistakes, no vomiting or diarrhea, no antibiotics, no drugs from a certain list, no St John's Wort. alcohol doesn't matter unless it makes you miss or delay a pill, etc.

If you're on the Pill having sex a few times a week for a year with someone on suppression, you're less likely to catch herpes than you are to get pregnant, unless your use of the Pill is "perfect".

Herpes suppression is better than condoms at preventing transmission.

One study found how unprotective condoms actually are:

  • For herpes, condoms provide little to NO protection to men
  • For herpes, condoms provide MINIMAL protection to women

While you can use condoms in combination with suppression, the suppression is already doing a huge amount of good, and condoms have little to contribute.

Many STD clinics don't test for herpes.

It's too expensive, too many people already have it to bother, etc. It still lets a person claim to have been tested for everything they test for without finding out (or telling you) about herpes.

A herpes blood test at a doctor's is needed to know.

There's a nearly 18% chance of someone having HSV-2 if they've had lots of sex with even only 2 to 4 people who weren't themselves virgins. And there's an 80% chance the person doesn't know, and an 80% chance that the partner who gave it to them doesn't either. You can't trust anyone's impression they're herpes-free without a blood test.

Note that this doesn't take into account false negatives/positives for these tests.

The lowest risk person to have sex with may not be who you'd expect.

Here's the list from safest first to riskiest last:

Risk Per Sex Act Risk Per
100 Acts
Acts For
10% Risk
percent fraction Group Herpes status and other details
0% - Blood Tested A person found negative by blood test
(assuming no false negatives).
0%+ (low) Virgins Some get infected through nonsexual contact, often by oral/HSV-1 (low) (lots)
0.06% 1 in 1666 Suppressors Those on suppression therapy. Be sure they're taking it daily. 5.8% 175
0.4% 1 in 250 Think Not Those who thinks they don't, aren't tested, see no need to get tested, etc.
Around one in seven+ of them is wrong with a 1 in 30 transmit chance.
33.0% 26
1.1% 1 in 90 Careful Those who know they do, are NOT on suppression, and avoid sex around times of prodrome, outbreak, stress, etc. 67.3% 9
3% 1 in 30 Careless Those who know they do, and ignore it entirely. 96.6% 3

So basically you're safer having a fling with a someone on suppression than you are with most people (the Think Not, Careful, and Careless groups).

For long term relationships, get a blood test (if you don't know) to see if caution will even matter.
...and remember that condoms you used only protected you a little.
...and any he used with other woman barely protected him at all.

To be fair, starting a long term relationship has different statistical dynamics. Supposing you're a woman for a moment: Over, say, a ten-year sexual relationship, the odds are that you'll catch whatever he has. At that point, if you chose a random man from the men who don't think they have HSV-2, he had a 20%+ chance of having it (substantially more for the hispanic and black social - not genetic - groups) combined with the 20%+ chance that you had it already (e.g. for women with 2-4 sex partners ever) and just gave it to him. This basically means that long term couples of Think Not people have 36%+ chance of both having herpes (60%+ if they both had 5+ partners, etc), though with a good chance of having noticed if one caught it from the other. However, becoming an Think Not carrier yourself isn't much of a life impact if you're asymptomatic. Futher, taking a tablet a day for suppression might just pair with taking daily vitamins anyway, and your health insurance might cover it 100%.

You can estimate your safety factor with math.

If you're planning on N sexual acts with someone with HSV-2 on suppression, you can compute the overall safety factor by taking the chance of being safe once, such as 1665/1666, 249/250, 89/90, or 29/30, and multiplying N copies of the dividend together. Subtract the safety factor from 1.0 to get the risk factor.

safety= (1665/1666)N
risk = 1 - (1665/1666)N

Example safety (still clear ratio) for once weekly sex acts for a year with someone on suppression:

safety= (1665/1666)52
= 0.969…
= 96.9 % chance to still be clear

Example risk from having sex three times per day for a year (1095 times) with someone on suppression

risk= 1 - (1665/1666)1095
= 0.4818…
= 48 % chance of transmission

To figure out how many times you can have sex together and stay at or below a given risk factor - as in your prospective partner isn't willing to take more than a 10% risk, and you want to see how many times that translates to - convert the risk percentage a safety ratio, then take the log (in base per-act-safety) of that safety ratio.

acts= logper_act_safety(safety)

Examples for 10% risk (= 90% safety) for Careless and Suppressor groups:

acts= log29/30(0.9)
= 3.1 acts with a careless person = 10% risk
acts= log1665/1666(0.9)
= 175.5 acts with a suppressor = 10% risk

(What the .1 and .5 might be is left as an exercise for the reader.)

Sources (partial):

  • Planned Parenthood:
  • National Center for Biotechnology Information (government site):
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