The need for a herpes vaccine is clear: about half a billion people worldwide between the ages of 15-49 have genital herpes infection caused by either HSV-1 or HSV-2, according to the World Health Organization (WHO). In the United States alone, an estimated 1 in 6 adults have genital herpes, with around 300,000 new infections diagnosed each year.
While HSV is typically a mild infection, there are potential health risks associated with it, including neonatal herpes, a serious and sometimes fatal condition that occurs when HSV is passed to an infant during delivery. Another concern is the increased risk of HIV infection. The risk of getting HIV (if exposed) is increased 2-3 fold for someone with genital HSV-2 infection.
Researchers have been working on developing herpes vaccines for decades. There have been a number of clinical trials aimed at testing both therapeutic (intended to reduce recurrences and viral shedding in people who are already infected with HSV) and preventive (designed to prevent infection) vaccine candidates. The largest to date was the Herpevac Trial for Women, a clinical trial done with over 8,300 women who were uninfected with either HSV-1 or HSV-2. The results of this prevenative vaccine were mixed: the vaccine was effective only in preventing HSV-1, not HSV-2. Because of these results, development of the vaccine was abandoned after Phase III of the clinical trial.
How do clinical trials work?
Before a treatment regimen or vaccine can become standard, it must go through a clinical trial. Clinical trials test if a potential treatment or vaccine is safe and effective in humans. Clinical trials go through a series of phases, starting with a smaller group of patients and expanding to a much larger group. The video explains the three main phases of a clinical trial.
Herpes Vaccine Clinical Trials
While the primary focus with herpes vaccine research is on HSV-2, the primary cause of genital infection, HSV-2 vaccines may also have benefits in preventing or treating HSV-1 infection. More information on those listed below and other clinical trials can be found at ClinicalTrials.gov, a resource of the National Library of Medicine.
“One can argue that HSV prevention overlaps public health and medical science with matters of justice.”
–ASHA president and CEO Lynn Barclay explains why we need an HSV vaccine.
- HSV529: Clinical trials for this HSV-2 vaccine candidate are examining both preventive and therapeutic applications. HSV529 uses a replication-defective mutant virus, which is genetically altered to prevent the virus from replicating. In the first phase, researchers are studying the safety of HSV529 vaccine and the ability of the vaccine to elicit immune responses to HSV-2 including virus-specific antibodies and T cell responses to the virus. Results to date have found the vaccine is safe and leads to a significant immune response against HSV-2.
Research with two HSV vaccine candidates that were once thought to be promising was discontinued after phase II trials. The company developing the GEN-003vaccine suspended the project in 2017 for business reasons. Results from phase 2 trials with another vaccine, VCL-HB01, were disappointing and did not demonstrate effectiveness in reducing recurrent outbreaks. The research was subsequently stopped.
For more on the current status of herpes vaccine development, including vaccine candidates in the preclinical phase, see this article prepared for the WHO Product Development Vaccine Advisory Committee.