Daily antiviral medication, usually valacyclovir (Valtrex), lowers the chance of passing genital herpes to a partner by a lot, but it does not bring the chance to zero.1CDC Sexually Transmitted Infections Treatment Guidelines. Genital Herpes Herpes can spread on days when there are no sores at all, and the pills reduce those days without ending them. The medicine works best as one layer of protection among several, not as a guarantee.
How Much Daily Valacyclovir Lowers the Risk
The best evidence comes from couples where one partner has genital herpes (HSV-2) and the other does not. When the infected partner took 500 mg of valacyclovir once a day, the uninfected partner’s risk of catching herpes over about 8 months fell from 3.6% to 1.9%.2PubMed. Once-Daily Valacyclovir to Reduce the Risk of Transmission of Genital Herpes Infections that caused noticeable symptoms dropped from 16 people to 4 out of about 740 in each group, about a 75% drop.3PubMed. Once-Daily Valacyclovir to Reduce the Risk of Transmission of Genital Herpes So the medicine is especially good at keeping a partner from getting outbreaks of their own.
For one couple, “halves the risk” is less dramatic than it sounds. Even without pills, most partners in the trial did not catch herpes over those 8 months. Protection adds up over months and years, so long-term couples gain the most. And it is still possible to catch herpes from a partner who takes the pill perfectly.
US health guidelines recommend 500 mg of valacyclovir daily to reduce transmission for couples where one partner has a history of genital HSV-2.4CDC Sexually Transmitted Infections Treatment Guidelines. Genital Herpes Doctors call taking the pill every day suppressive therapy.5CDC Sexually Transmitted Infections Treatment Guidelines. Genital Herpes
The trial enrolled heterosexual couples where the infected partner had HSV-2, so the numbers are strongest for that situation. Other couples, such as same-sex couples, were not the focus, so the exact size of the benefit is less certain for them, and the same goes for HSV-1. The drug works the same way in the body, though, and guidelines still offer daily medication to many people outside the trial group because the way it lowers shedding is not specific to one kind of couple.
Valacyclovir is not a cure. It does not remove the virus from the body, and stopping the pill brings shedding back to its usual level within days. Missing doses lowers protection, so a daily routine matters.
To start, ask a doctor about daily suppressive therapy specifically for protecting a partner. Mention any kidney problems and any other medicines you take. Ask how long to stay on it and when to review the plan. Prescriptions are usually generic and widely available.
Why Herpes Spreads Without Sores and What the Pills Do About It
Viral shedding means live virus is present on the genital skin, and it often happens with no sore or feeling at all. Sensitive tests show it is more frequent than older tests suggested.6PubMed. HSV shedding In people newly diagnosed, shedding without symptoms happened on about 11% of days without treatment.7PubMed Central. Once Daily Valacyclovir for Reducing Viral Shedding in Subjects Newly Diagnosed with Genital Herpes Because most transmission happens during these unnoticed days, a partner can be infected by someone who feels fine.
Because you cannot tell by looking or feeling whether you are shedding that day, feeling fine is not a safety signal. It is also why the pill helps even people who rarely get outbreaks, and why condoms add protection on top of it.
On daily valacyclovir, silent shedding in newly diagnosed people fell to about 2.4% of days, a 78% drop.8PubMed Central. Once Daily Valacyclovir for Reducing Viral Shedding in Subjects Newly Diagnosed with Genital Herpes In the couples trial, the infected partner’s shedding fell from about 11% of days to about 3%.9N Engl J Med. Once-daily valacyclovir to reduce the risk of transmission of genital herpes People who carry HSV-2 but have never noticed an outbreak shed too, and daily pills cut their silent shedding by about 71%.10PubMed. The effect of daily valacyclovir suppression on herpes simplex virus type 2 viral shedding in HSV-2 seropositive subjects without a history of genital herpes Of those people, 84% had no shedding detected at all while on the pill, compared with 54% without it.11PubMed. The effect of daily valacyclovir suppression on herpes simplex virus type 2 viral shedding in HSV-2 seropositive subjects without a history of genital herpes
Valacyclovir turns into acyclovir in the body, which blocks the virus from copying its genetic material inside cells. Fewer copies means less virus reaching the skin. The drug cannot reach the virus resting in nerve cells, which is why it is not a cure.
Even at high doses, short bursts of shedding still happened on medication.12PubMed Central. Ineffectiveness of daily standard and high-dose antiviral therapy in preventing short episodes of genital HSV-2 reactivation: three randomized, open-label cross-over trials These bursts usually lasted under half a day, and 80% caused no symptoms.13PubMed Central. Ineffectiveness of daily standard and high-dose antiviral therapy in preventing short episodes of genital HSV-2 reactivation: three randomized, open-label cross-over trials
Daily Pills Versus Taking Them Only During Outbreaks
Episodic therapy means taking pills only when an outbreak starts, to shorten it. Only daily treatment has been tested for protecting partners, so no one should assume outbreak-only treatment gives the same benefit.
The outbreak numbers differ a lot too. Over a year, people on outbreak-only treatment had about 8 outbreaks versus about 1.6 on daily pills.14PubMed. A comparison of one year of episodic or suppressive treatment of recurrent genital herpes with valacyclovir They also had more days with pain and sores, about 6.5 days versus about 1.15PubMed. A comparison of one year of episodic or suppressive treatment of recurrent genital herpes with valacyclovir
Daily medication suits people with a regular partner or frequent outbreaks. Outbreak-only treatment may suit those with rare outbreaks and no partner at risk. People can switch as life changes, such as a new relationship.
The tested schedule is one 500 mg pill a day. Some people with very frequent outbreaks are given a higher dose.
Other Steps That Lower the Risk Alongside Medication
Combining medication with condoms, disclosure, and partner testing gives a partner the greatest protection.16Canada.ca. Genital herpes counselling tool Avoiding sex from the first tingle until sores have fully healed removes the highest-risk days. Those are the days with sores or the early tingling that often comes before them, and pills do not make sex during an outbreak safe, because sores carry a large amount of virus. Wait until the skin looks normal again.
Condoms do not cover all skin that can shed, so they reduce risk rather than remove it. They work best when used every time, from the start of sex, including oral and anal sex where herpes can also pass.
A blood test can show whether a partner already has HSV-1 or HSV-2. If the partner already has the same type, a new infection with that type is unlikely, so the medication matters less for protecting them. Ask for type-specific blood testing, since routine STI panels often skip herpes. Telling a partner lets them make an informed choice.
Daily HIV prevention pills (PrEP) lowered the chance of catching HSV-2 by about 30% in heterosexual couples.17CDC Sexually Transmitted Infections Treatment Guidelines. Genital Herpes Among people whose partner already had HSV-2, PrEP cut their yearly risk by about 3 infections per 100 people.18PubMed. Daily oral tenofovir and emtricitabine-tenofovir preexposure prophylaxis reduces herpes simplex virus type 2 acquisition among heterosexual HIV-1-uninfected men and women: a subgroup analysis of a randomized trial A tenofovir vaginal gel used around sex lowered women’s risk of catching HSV-2 by about half in one study.19PubMed Central. Tenofovir-based Pre-Exposure Prophylaxis for HIV Prevention: Evidence and evolving questions These are not prescribed for herpes alone.
Oral Herpes and Genital HSV-1
More new genital herpes cases now come from HSV-1, often via oral sex. Many people catch HSV-1 as children or young adults as a cold sore, so they carry the virus in their mouth. Oral sex can pass it to a partner’s genitals, even when the person giving it had no visible cold sore. That is why a partner with a history of cold sores can matter for genital herpes.
After a first genital HSV-1 infection, the virus was found on about 12% of days at 2 months, falling to 7% at 11 months.20PubMed Central. Viral Shedding 1 Year Following First-Episode Genital HSV-1 Infection21PubMed Central. Viral Shedding 1 Year Following First-Episode Genital HSV-1 Infection Genital HSV-1 sheds less over time than HSV-2, so long-term risk may be lower. People who already have HSV-1 are also about half as likely to have HSV-2.22PubMed Central. Negative epidemiological association between HSV-1 and HSV-2 infections
The couples trial only tested HSV-2, so protection for HSV-1 is assumed, not proven. Because the drug lowers shedding of both types, doctors often still offer it. Avoid oral sex during cold sores. Ask a doctor whether daily pills are worthwhile for you.
Herpes Medication in Late Pregnancy
Herpes passed to a newborn during birth can be very serious. A baby is exposed mainly while passing through the birth canal, which is why shedding at delivery matters most.
Women with known genital herpes who took antivirals in late pregnancy were about 70% less likely to have an outbreak at delivery.23Cochrane Database of Systematic Reviews. Interventions for herpetic recurrences in late pregnancy They were about 86% less likely to have virus detected at delivery.24Cochrane Database of Systematic Reviews. Interventions for herpetic recurrences in late pregnancy They were also about 70% less likely to need a cesarean because of herpes.25Cochrane Database of Systematic Reviews. Interventions for herpetic recurrences in late pregnancy In one study, shedding at delivery fell from 5% to near 0% with preventive pills.26PubMed. Acyclovir prophylaxis in late pregnancy prevents recurrent genital herpes and viral shedding
Tell your prenatal provider about any herpes history, even if outbreaks were years ago or you were never diagnosed by a test. A partner’s herpes history is worth mentioning too, since it affects the risk of a first infection during pregnancy.
Preventive pills usually start around 36 weeks. Report any symptoms near labor. The biggest risk to the baby is a first infection late in pregnancy, so a partner with herpes should take extra care, such as avoiding sex or oral sex when there is any chance of passing it on, during the last months.
Newer Drugs Being Tested
An experimental drug, pritelivir, has cut shedding more than valacyclovir. In people with frequent outbreaks, virus was found on 2.4% of swabs with pritelivir versus 5.3% with valacyclovir, about half as much.27PubMed. Effect of Pritelivir Compared With Valacyclovir on Genital HSV-2 Shedding in Patients With Frequent Recurrences: A Randomized Clinical Trial Sores appeared on 1.9% of days versus 3.9%.28PubMed. Effect of Pritelivir Compared With Valacyclovir on Genital HSV-2 Shedding in Patients With Frequent Recurrences: A Randomized Clinical Trial Days with pain were 4% versus 6.7%.29Fred Hutch. Experimental herpes drug pritelivir more effective than standard treatment These were people with frequent outbreaks, so the results may not apply to someone with rare ones.
Pritelivir blocks a different step in the virus’s life cycle, a helper protein the virus needs to copy itself. Because the target is different, it has been studied in people whose herpes no longer responds well to older drugs.
Safety concerns in animal studies mean more research is needed before it is available.30Fred Hutch. Experimental herpes drug pritelivir more effective than standard treatment It is not available outside studies, and valacyclovir remains the standard daily option. Whether pritelivir reduces partner infections has not been tested.