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.

Herpes virus
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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.

Existing Herpes Vaccines

Technically speaking, several herpes vaccines already are on the market. 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 two vaccines currently available protect against a herpes virus known as varicella-zoster virus (VZV). This is the virus responsible for chickenpox. Once the chickenpox infection resolves, the virus remains in a latent (dormant) state in a cluster of nerve cells called the dorsal root ganglion where it can reactive in later life to cause shingles (herpes zoster).

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

  • The chickenpox vaccine is typically given in early childhood to protect you from becoming infected with VZV.
  • The shingles vaccine is given from the age of 50 to prevents the reactivation of VZV.

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 aims to protect against outbreaks in people who already have herpes.

The latter is especially important because once you are infected with a herpes virus, it stays in your body forever. The virus is not cleared but remains in a latent state where it can suddenly and sometimes inexplicably reactivate.

This is why the virus that causes chickenpox can suddenly reactivate during adulthood to cause shingles, or why oral or genital herpes outbreaks can recur.

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:

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

The 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.

Challenges

Scientists have several hurdles to face when developing a vaccine to protect against oral or genital herpes.

One of the challenges is that no animal model perfectly replicates HSV infection in humans. Several vaccine candidates have shown promise in animal studies but have thus far not been effective in clinical trials in humans.

Aside from mice, rabbits and guinea pigs are also being used to develop therapeutic herpes vaccines (for ocular and genital herpes, respectively). And, while early results have been promising, current animal models still fall short in simulating the disease processes and progression 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.)

Advances

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 the research, a genetically modified form of herpes simplex virus type 1 (the type most commonly associated with oral herpes) was able to 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.

Another researcch team at the Irvine School of Medicine in California proposed the use of lasers as part of the vaccination procedure. Their goal was to stimulate the development of immune cells in the layers of the skin where herpes reactivation occurs. The procedure involving mice again showed promised in preventing genital herpes, amplifying the effect of an experimental vaccine.

Although it is far too soon to predict whether either of these studies will lead to a viable vaccine candidate, these advances are seen as significant.

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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