Vaccine Fails to Protect Against Herpes Infection

A promising shot against herpes virus misses the mark. But antiviral drugs can control infection, if only for a short time

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Encouraged by the success of vaccines against human papillomavirus, researchers began developing a shot that they hoped would immunize women against another sexually transmitted virus, herpes. But the latest results, reported in the New England Journal of Medicine, aren’t encouraging.

The vaccine was designed to protect women against two forms of herpes, HSV1 and HSV2, and involved more than 8000 women between ages 18 and 30. Previous studies had shown the shot provided some protection against infection with the viruses, but the latest trial revealed that the vaccine was only mildly effective in preventing HSV-1 infections and not protective at all against HSV-2. None of the women had herpes at the start of the study, and were followed for 20 months to see if three doses of the shot prevented herpes infection due to normal sexual activity. Half of the women received the hepatitis A vaccine, which served as a control.

“I think this is the end of the vaccine,” the study’s co-author Dr. Peter Leone, an infectious disease expert at University of North Carolina Chapel Hill told

MORE: How Many Patients Spread Herpes, But Don’t Even Know They Have It?

The study wasn’t a complete waste, however, since the researchers learned some new things about herpes infections that could improve future treatments. Most experts had thought that HSV-1 was primarily responsible for cold sores, while HSV-2 contributed to blisters on the genitals. The study showed, however, that women who didn’t receive the vaccine were more likely to contract genital herpes due to HSV-1.

That means that a vaccine able to protect against both HSV-1 and HSV-2 will be critical, and Leone and his team already have some ideas about how to develop one. While the current shot included snippets of herpes virus protein to alert the immune system, a more effective vaccine may need a more robust trigger, such as a weakened form of the virus, to elicit a proper virus-killing response.

In the meantime, there are drugs that can reduce the symptoms of herpes infections. In a study reported in the journal Lancet, scientists say that anti-viral drugs such as valacyclovir (Valtrex) and acyclovir (Zovirax) can lower the amount of HSV-2 virus shed in the body during infection. The effect isn’t long lasting, but can help in lowering risk of transmission. That’s why a vaccine is so important to truly control spread of the virus. According to the Centers for Disease Control, 16% of Americans between 14 and 49 are infected with HSV-2.