HSV-2 Asymptomatic Shedding: How Often and What Cuts It

Shedding is the reason HSV-2 is so common, and the reason so many people catch it from someone who honestly had no idea. It is also the part of herpes that worries people most after a diagnosis, because you cannot see it and you cannot feel it. This page puts real numbers on it. Every figure comes from studies where people swabbed themselves every day, sometimes four times a day, and the swabs were tested in a lab.

What shedding actually is

After the first infection, HSV-2 lives quietly in a cluster of nerve cells near the base of the spine. Every so often it wakes up, travels down the nerve to the skin, and makes copies of itself on the surface. That is shedding. Sometimes the immune system lets it get far enough to cause a blister or sore, and that is an outbreak. Much more often the immune system clears it within hours, before anything shows. That is asymptomatic, or subclinical, shedding.

The word “asymptomatic” gets used in two ways, which confuses a lot of people. It can describe a day (you are shedding but have no symptoms that day), or a person (someone who has HSV-2 and has never noticed an outbreak). Both matter, and the numbers below cover both.

How often it happens

The biggest study followed 498 people with HSV-2 who swabbed every day for at least 30 days. Here is what it found, alongside a second study that looked at how shedding changes over the years (Tronstein 2011, Phipps 2011).

Group	Days with any virus	Days with virus but no sores
Has had genital symptoms	20.1%	13.1%
Has never had symptoms	10.2%	8.8%
First year after first outbreak	33.6%	26.2%
1 to 9 years after	20.6%	13.1%
10 years or more after	16.7%	9.3%

Put simply, someone who has had outbreaks has virus on the skin roughly one day in five, and about two thirds of those days come with no sore at all. Someone who has never noticed symptoms sheds about half as often, but on almost every one of those days there is nothing to see.

People with no symptoms shed too

This is the single most important finding for anyone wondering how they caught HSV-2. In the JAMA study, the 88 people who had never had a recognised outbreak still had virus on 10.2% of days. And when they did shed, the amount of virus was the same as in people who get outbreaks: a median of 4.2 log copies compared with 4.3 (source).

In other words, a partner who has never had a sore in their life can carry as much virus on their skin on a shedding day as someone in the middle of an outbreak. They are not lying when they say they have never had herpes. They simply never knew.

How long an episode lasts, and why you cannot feel it

Researchers at the University of Washington had people swab four times a day for 60 days to catch episodes that a once a day swab would miss. About a quarter of genital episodes (24%) were over within 6 hours, and about half (49%) were over within 12 hours. Only 7% of those short episodes came with any sore at all (source).

A later study found that without medication, people had about 28.7 separate shedding episodes a year, with a typical episode lasting 13 hours. Around 80% of all episodes caused no symptoms, whatever medication people were on (source).

So shedding is not a few long stretches a year. It is many short bursts, most of them over before the end of the day, and most of them completely silent. That is why there is no reliable way to tell when you are shedding. Some people notice tingling or itching before an outbreak, which is called a prodrome, and it is sensible to avoid sex then. But the absence of a prodrome does not mean the absence of virus.

When shedding is highest

• During and around an outbreak. In people who get outbreaks, the days with sores made up 43% of all their shedding days (source). Sores are the most infectious time by a wide margin.
• In the first year. Shedding drops from about 34% of days in the first year to about 21% in the years after and 17% after a decade (source). It falls, but it never reaches zero.
• In people who get frequent outbreaks. The more often the virus wakes up enough to cause sores, the more often it wakes up without causing them too.

One thing that does not lower the amount of virus is time. The same long term study found the quantity of virus on shedding days barely changed between the first year and ten years on (source). Shedding gets less frequent, not weaker.

What actually cuts shedding

Daily antiviral medication is the only thing proven to reduce shedding by a large amount. In a three way crossover trial of 69 people, the same people took valacyclovir, acyclovir and a placebo for seven weeks each (source).

Regimen	What happened to shedding	Source
No medication	Virus found on 40.2% of days by sensitive PCR testing	Gupta 2004
Valacyclovir daily	82% less shedding than placebo	Gupta 2004
Acyclovir daily	80% less shedding than placebo, no real difference from valacyclovir	Gupta 2004
Acyclovir 400 mg twice daily	Episodes fell from 28.7 to 10.0 a year and lasted 7 hours instead of 13	Johnston 2012
Valacyclovir 1 g three times daily	Swabs positive 3.3% of the time compared with 5.8% on 500 mg daily, with more headaches	Johnston 2012

Two things stand out. First, valacyclovir and acyclovir are about equally good at this job. Valacyclovir is easier because it is once a day, but acyclovir taken properly works almost as well. Second, even very high doses leave some short bursts behind. The authors of the Lancet study concluded that these short bursts probably explain why people on suppressive therapy can still occasionally pass the virus on (source).

Does suppressive therapy make you safe for a partner?

Safer, not risk free. In the trial that settled this question, daily valacyclovir 500 mg cut the chance of passing HSV-2 to a partner by about 48% over eight months (source). Shedding falls by more than 80%, yet transmission only falls by about half, which tells you that the bursts that remain are enough to infect someone now and then.

That is why the CDC recommends suppressive therapy alongside condoms and avoiding sex during outbreaks, not instead of them (source). Each step removes a different part of the risk. Our transmission guide goes through the combined numbers, and our one time exposure guide works out the odds per act.

What could cut it further

The most promising result in years came from a once a week pill called ABI-5366, which reduced HSV-2 shedding by 94% compared with placebo in a small Phase 1b trial. It still needs larger trials before it could be approved. We follow it, and every other drug and vaccine in development, on our vaccine and cure tracker.

What this means for you

• If you were just diagnosed and do not know where it came from: shedding is the most likely answer. Your partner may never have had a symptom. Our newly diagnosed guide covers the first week.
• If you want to protect a partner: daily antivirals, condoms and skipping sex during outbreaks or a prodrome together give far more protection than any one of them. See our valacyclovir guide for doses and cost.
• If you are in your first year: this is when shedding is highest, so it is the year when suppressive therapy does the most good.
• If you have had HSV-2 for many years: you still shed, just less often. Disclosure still matters, and our disclosure guide has scripts that help.

Related: How HSV-2 spreads | Risk from one encounter | Valacyclovir guide | HSV-2 and oral sex