Clinical trials that looked promising did not produce the anticipated results. So, companies are moving on to other medications such as cancer vaccines.

Clinical trials for a herpes vaccine that looked so promising in 2017 have fizzled.

Two companies have announced they are no longer actively pursuing a herpes vaccine after results from their clinical trials.

A third company in the midst of clinical trials outside the United States has become embroiled in a federal investigation.

In June of 2018, executives at Vical Incorporated announced the phase II clinical trial for their herpes simplex virus type 2 (HSV-2) did not meet “its primary endpoint.”

“We are extremely disappointed with the outcome and based upon these results, we will be terminating the HSV-2 program,” said Vijay Samant, president and chief executive officer for Vical, in a press release. “We are indebted to our patients for their participation and our investigators for their steadfast support.”

Samant said the biopharmaceutical company instead will be pursuing an antifungal drug that is currently in a phase II clinical trial.

In September of 2017, executives at Genocea announced they were exploring “strategic alternatives” for its herpes vaccine known as GEN-003.

A phase II trial had been completed and an eagerly awaited phase III trial had been scheduled to begin.

However, in the September announcement, Genocea officials said they were ceasing GEN-003 spending and reducing the project’s workforce by 40 percent.

Instead, the company made a “strategic shift” to the development of neoantigen cancer vaccines.

“[This] gives us the opportunity to create value for our shareholders by developing best-in-class vaccines for cancer patients and achieving leadership in this exciting field,” said Chip Clark, president and chief executive officer of Genocea, in a company press release.

In addition, Rational Vaccines’ experiments with its potential herpes vaccine is apparently in legal hot water.

Kaiser Health News reported in April of 2018 that the Food and Drug Administration (FDA) had launched an investigation into experiments in the Caribbean islands in 2016, where participants had been injected with the experimental herpes vaccine without safety oversight.

The probe is reportedly centered around the actions of William Halford, a college professor and co-founder of Rational Vaccines, who died a year ago.

In March of 2018, three people who participated in experiments overseen by Halford filed a lawsuit against Rational Vaccines over the side effects they said they suffered, according to Kaiser Health News.

The developments at all three companies apparently leaves the scientific world without a major research effort for a herpes vaccine.

The herpes simplex virus (HSV) affects many people worldwide. The World Health Organization (WHO) estimates that 67 percent of people under the age of 50 are infected with HSV-1 while 11 percent of people between the ages of 15 and 49 are infected with HSV-2.

Right now, antiviral drugs, including acyclovir (Zovirax), famciclovir (Famvir), and valacyclovir (Valtrex) are the some of the treatments approved by the FDA that people can take to fight HSV.

It’s worth noting that HSV is different than the human papillomavirus (HPV). Herpes comes with a host of symptoms, including blisters, itching, and red bumps. HPV, on the other hand, often causes no symptoms at all.

“Herpes is a very smart bug,” Dr. Jamin Brahmbhatt, a urologist with Orlando Health in Florida, told Healthline in August 2017. “With most vaccines, the way they work is they use your immune system to basically build a tolerance against, or an immunity against, whatever you’re exposed to with the vaccine… Herpes has kind of learned ways to bypass your immune system. So it’s a lot more difficult to target when it comes to vaccines.”

However, HSV and HPV also share some commonalities.

They can both be difficult to treat.

They’re also widespread, affecting millions of people in the United States and billions around the world.

But while there’s a vaccine available in the United States able to prevent HPV, there isn’t one available to treat or prevent HSV.

“It’s [HSV] very prevalent, and I’d say the numbers are probably higher than the statistics would indicate,” said Brahmbhatt. “And that’s why there’s a big focus on — number one — how can we prevent someone from contracting the actual virus to avoid some of these complications? And — number two — if you’ve contracted the virus already, what can we do to control the symptoms? Because all we have right now is one class of medication that helps control the symptoms. But is there a way that we can do that better? Those are the mentalities that are going into finding some sort of vaccine.”

Hopes for a herpes vaccine haven’t completely been extinguished. The pharmaceutical company Sanofi Pasteur has been conducting clinical trials on a potential HSV-2 vaccine. So far, the results of an early trial have been promising and further studies are underway.

The vaccine is called HSV529. HSV529 is a strain of HSV-2 in which two important viral proteins have been deleted. Because of this, HSV529 can infect cells, but cannot replicate to make more copies of itself.

A phase I clinical trial was conducted to assess the safety of HSV529 in people without HSV infection or people with HSV-1 and/or HSV-2 infection.

Results indicated that HSV529 was safe and led to an immune response in HSV-negative participants when compared to a placebo vaccine.

A second phase I clinical trial was completed in late 2018. Its aim was to further evaluate the safety of HSV529 in people with HSV-2 and to see if the vaccine increased the immune response to HSV-2 in the genital skin.

Participants entered the study when they had a genital herpes outbreak due to HSV-2. Initial biopsies were taken from skin with herpes sores and from skin without sores. Participants were then given the antiviral drug valacyclovir for one month, after which the HSV529 vaccine was given.

An additional dose of HSV529 vaccine was given after one month and again after six months. Biopsies from the sites with and without sores were collected throughout the trial as well as blood samples and genital swabs for additional testing.

So far, the results for this new trial haven’t been reported. Despite the early stages of the research, investigators are hopeful that this recent trial, as well as further trials on HSV529, will result in a HSV-2 vaccine.

Editor’s note: This piece was originally reported on August 29, 2017. Its current publication date reflects an update, which includes additional reporting by Jill Seladi-Schulman, PhD, and a medical review by Karen Gill, MD.