A viable herpes vaccine could certainly provide a lucrative financial windfall for the company that develops it.

After all, the herpes simplex virus affects about two-thirds of the population worldwide under the age of 50.

However, no company has developed a commercially ready vaccine despite some concerted efforts.

In fact, at least three companies that were overseeing clinical trials on a herpes vaccine last year have since abandoned their research.

And, at the moment, there’s no major clinical trial under way for a vaccine to prevent the sexually transmitted disease.

So, why can’t the pharmaceutical industry develop a herpes vaccine after decades of trying and hundreds of millions of dollars in investment?

We have vaccines for measles, mumps, hepatitis B, and whooping cough. Why not herpes?

Experts tell Healthline there are a number of reasons.

First, the herpes virus is quite complicated.

It’s also similar to cancer in the way it can go undetected by the body’s immune system.

In addition, the virus can lay dormant in a person’s body for years before springing to life and making somebody sick.

And it has a lot of company among sexually transmitted diseases such as syphilis and gonorrhea that also don’t have vaccines.

“Herpes does not stand alone,” Dr. William Schaffner, chair of the Department of Preventive Medicine at Vanderbilt University Medical Center in Tennessee, told Healthline.

The herpes virus

The herpes simplex virus (HSV) is the infection that causes herpes.

There are two types of the virus.

One is HSV-1, also known as oral herpes. It causes cold sores and fever blisters around the mouth and face.

The second is HSV-2, also known as genital herpes. This can cause sores in the genital area or pain during urination.

HSV-1 is contracted through contact such as kissing, eating from the same utensils, and sharing lip balm.

HSV-2 is spread through sexual contact.

Once the virus is in a person’s system, it stays there for life. People can also be infected with the virus and have no symptoms.

Right now, the sores and other symptoms of herpes are treated with one of several antiviral medications.

There is no cure and there is no preventative treatment such as a vaccine.

A difficult battle

The structure and behavior of the herpes virus is what makes it difficult to develop a vaccine.

“The herpes virus is very different from the measles virus, for example,” said Schaffner.

He explains the measles virus makes you sick in a relatively short period of time. Our immune system reacts quickly to it and is ready for the virus again should it appear in the future.

The herpes virus, however, doesn’t always present itself immediately.

“It’s hibernating within our body and then periodically reoccurs,” Schaffner said.

The herpes virus has more complicated DNA than most infections and has ways to go undetected by our immune system, much like many cancer cells do.

Since vaccines work by stimulating the human immune system, this makes it more difficult to develop an inoculation for herpes.

“It makes it hard to develop a vaccine because you don’t know what the target is,” said Schaffner.

Dr. Ashley Thomas, an infectious disease specialist at Orlando Health in Florida, notes that the herpes virus has evolved along with humans over the centuries.

That means it is more like a guest inside our body than an invader.

“The virus is highly capable in evading our immune system,” Thomas told Healthline.

Corporate reluctance

All these barriers make developing a herpes vaccine a double-edged sword for pharmaceutical and biomedical companies.

The fact the virus is so common makes the vaccine a potentially lucrative product.

The fact the virus is so complicated makes research expensive and lengthy.

“We’ve had a lot of false starts on this,” noted Schaffner. “There have been some big investments that haven’t panned out.”

One of those was the phase II clinical trial last year involving Genocea Biosciences’ GEN-003 herpes vaccine.

The trial produced some positive results, but it wasn’t enough to persuade company executives to move forward.

Instead, Genocea has cut the GEN-003 program and is looking to “license out” its infectious disease programs to a partner.

The company is now focusing on the immuno-oncology area of cancer research.

On a “Long Run with Luke Timmerman” podcast in May, Genocea Chief Executive Officer Chip Clark said his company was initially excited about developing a herpes vaccine.

They felt there was a great need to develop such a vaccine, and a market for the product was there if it was produced.

However, Clark said a phase III trial would have cost $150 million and taken three years. In the end, the company’s board and investors were “unwilling to take on the investment.”

Schaffner said more basic research to get a better understanding of the herpes virus may be needed before companies are willing to sink hundreds of millions of dollars into a vaccine.

“Companies usually don’t do all the front-end research,” he said.

Thomas added that researchers will have to come up with some different strategies if a herpes vaccine is ever going to be produced.

“There might have to be some really new ideas,” he said.