Progress in Developing a Herpes Vaccine

The search for a vaccine to protect against oral and genital herpes has been a long one. Researchers have been experimenting with possible vaccines since at least the early 1930s. To date, they've seen little success. While herpes vaccines have been successful in mice, they've been largely unsuccessful in human trials.

Although some herpes vaccines have initially appeared to have promise, stringent testing has shown them to be no better than placebo.

With that said, newer approaches to vaccine development (including genetic editing) have begun to show promise in early-stage animal research, offering a glimpse of hope of a possible breakthrough.

Herpes virus
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Existing Herpes Vaccines

Technically speaking, several herpes vaccines already are on the market. However, while these vaccines protect against some viruses in the herpes family, they don't protect you from herpes simplex viruses (HSV), which cause genital or oral herpes.

The shingles vaccine and chickenpox vaccine both guard against herpes viruses but in different ways:

  • The chickenpox vaccine, or varicella-zoster virus (VZV) vaccine, protects you from ever becoming infected with VZV.
  • The shingles vaccine reduces the likelihood that an existing virus will reactivate and cause symptomatic shingles.

These are similar to the two types of vaccines that have been proposed to protect against oral and genital herpes. One type aims to prevent the virus from infecting people who've never had it, while the other type aims to protect against outbreaks in people who already have herpes.

Vaccine Priorities

Theoretically, it makes sense that a vaccine could work to prevent herpes outbreaks. After all, in many people, the immune system controls herpes infections so that they never have symptoms.

This makes the virus a good target for a therapeutic vaccine (one that treats rather than prevents disease). However, the herpes simplex viruses have proven to be difficult to control with vaccines.

In 2017, the World Health Organization (WHO) defined a series of priorities for developing a herpes vaccine. These priorities came out of a worldwide stakeholders conference focusing on important characteristics of a potential herpes vaccine.

The group of priorities that they came up with were:

  • To reduce the number of people who become infected with HIV because they have a herpes genital infection. (Genital sores increase the risk of HSV transmission). 
  • To reduce the number of people negatively affected by HSV. This includes reducing physical symptoms, psychological symptoms, and serious consequences such as neonatal herpes.
  • To reduce the impact of herpes infection on reproductive health.

WHO suggested that two types of vaccines could be useful for herpes simplex infections.

  1. Prophylactic vaccines, like the chickenpox vaccine, would help prevent people from ever getting herpes.
  2. Therapeutic vaccines, like the shingles vaccine, would reduce the number of outbreaks.

Herpes Vaccine Research

Some promising trials of herpes vaccines have been performed. However, to date, no human trials have shown high enough efficacy to bring a herpes vaccine to market.

Even so, there's still hope for vaccine development. Scientists have managed to protect some subgroups of people against herpes infection, and researchers continue to look for novel approaches.

One research group, for example, is using lasers as part of their vaccination procedure. Their goal is to stimulate immune cell development in the layers of the skin.

However, scientists have to face several hurdles when developing a herpes vaccine. The biggest is that there's no good animal model for testing vaccines.

Mice and guinea pigs can be infected with herpes, but their infections are quite different from human infections. This means vaccines that work for animals haven't been particularly successful in humans.

Herpes vaccines are also difficult to study for several other practical reasons:

  • Limited study population: You need to test a lot of people to see if they work. Those people can be hard to find.
  • Asymptomatic infection: Many infected people never have herpes symptoms, so with a preventive vaccine, you can't just wait to see if they ever have an outbreak. You have to actively test to see whether they've been infected with the virus since being vaccinated.
  • Viral shedding: For therapeutic vaccines, you have to test how the vaccine has affected the amount of virus they shed to determine the effectiveness of the vaccine candidate. (Low viral shedding translates to a lower risk of infection).

Addressing any of these factors can make vaccine trials both slow and expensive. Even so, a 2020 study from researchers at the University of Cincinnati, Northwestern University, and the University of Nebraska-Lincoln offered hopes of a possible breakthrough.

According to research published in Nature, a genetically modified form of herpes simplex virus type 1 (the type most commonly associated with oral herpes) was able to not only prevent symptoms of herpes simplex virus type 2 (the type most commonly associated with genital herpes) in guinea pigs.

The response was far more robust than seen with any herpes vaccine study to date, with significantly impaired viral replication and less viral shedding. Although it is far too soon to predict whether the same will occur in humans, the advance is seen as significant and may one day lead to an effective vaccine candidate.

A Word From Verywell

Around the world, doctors and scientists are aware that stopping herpes is a priority. Although many people infected with the virus have no symptoms, herpes can have a significant impact on people's lives. This is particularly true for those who become infected during pregnancy or who live in areas with a high incidence of HIV.

That's why herpes vaccine research is so important. However, there are no quick answers.

Fortunately, you have other options for reducing the risk of herpes transmission. Both suppressive therapy and reliably practicing safe sex can help protect the sexual partners of people with HSV infections.

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