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.

This article explains the steps that have been taken thus far to develop vaccines for oral and genital herpes, the reasons why these vaccines are important, and the roadblocks keeping researchers from better preventing or controlling herpes infections.

Where Herpes Vaccine Research Stands

Although some vaccines for these herpes types have initially appeared to have promise, stringent testing has shown them to be no better than a sham vaccine, or 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, there are already herpes vaccines on the market. They just don't protect you from herpes simplex virus (HSV) type 1 (the type most commonly associated with oral herpes) or HSV type 2 (the type most commonly associated with genital herpes).

Rather, the two vaccines currently available protect against a type of herpes virus known as varicella-zoster virus (VZV), more commonly called the chickenpox virus.

Once a chickenpox infection resolves, the virus remains in a dormant (latent) state. It does so in a cluster of nerve cells called the dorsal root ganglion, where it could reactivate later in life. If it does, it causes shingles (herpes zoster).

The shingles vaccine and chickenpox vaccine both guard against the virus, 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.

Protecting people who have had herpes from future outbreaks is important because once you're infected with a herpes virus, it stays in your body forever. It goes dormant, but can suddenly reactivate at any point, bringing on symptoms again.

An adult in their 60s, for example, might develop shingles due to a reactivation of VZV that they acquired when they had chickenpox as a child.

Oral and genital herpes outbreaks can recur in the same way.

Herpes Vaccine Priorities

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

This makes herpes a good target for a therapeutic vaccine—that is, 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:

• Reduce the number of people who become infected with human immunodeficiency virus (HIV) due to a herpes genital infection. (Having genital sores increases your risk of getting HIV.)
• Reduce the number of people negatively affected by HSV by reducing physical symptoms, psychological symptoms, and serious consequences such as infection in newborns (neonatal herpes).
• Reduce the impact of herpes infection on reproductive health.

The WHO suggests 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.

Barriers and Successes

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.

Aside from mice, rabbits and guinea pigs are also being used to develop therapeutic herpes vaccines (for eye and genital herpes, respectively). Early results have been promising, but current animal models still don't do a great job of showing how the disease progresses in humans.

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

• Limited study population: Researchers need to test a lot of people to see if a vaccine works. Those people can be hard to find.
• Asymptomatic infection: Because many infected people never have herpes symptoms, assessing the effectiveness of a preventive vaccine means having to actively test to see whether they've been infected with the virus since getting the shot.
• Viral shedding: Scientists have to test the possibility that the virus will be shed, or release particles that can infected others. Low viral shedding translates to a lower risk of infections.

Addressing any of these factors can make vaccine trials slow-going, burdensome, impractical, and expensive.

Advances

A 2020 study from researchers from the University of Cincinnati, Northwestern University, and the University of Nebraska-Lincoln offers hope of a possible breakthrough.

According to the research, a genetically modified form of herpes simplex virus type 1 was able to prevent symptoms of herpes simplex virus type 2 in guinea pigs. The response was far more robust than seen with any herpes vaccine study to date. It significantly slowed the virus's replication and showed less viral shedding.

Another research team at the University of California, Irvine, School of Medicine 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 involved mice. It, too, showed promise in preventing genital herpes, improving the effect of an experimental vaccine.

Although it's far too soon to tell whether the studies will lead to a successful vaccine, these advances are considered significant.

Summary

Putting an end to oral and genital herpes would have a far-reaching impact on the health of people around the world. The virus increases the risk of HIV, affects fertility, and places significant psychological and physical stress on those infected. 

Unfortunately, there are a number of barriers to developing a vaccine. First, it’s hard to find people who are able to participate in the studies needed to test possible vaccines. Also, people who are infected may not have symptoms, which makes it more complicated to tell whether a vaccine is effective.

A Word From Verywell

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