Genital Herpes Vaccine Partially Successful

Results of a clinical trial show that an investigational vaccine for genital herpes protected some women against infection from one of the two strains of virus that cause the disease. Although the results show only partial success, the researchers who conducted the trial believe they represent progress towards a genital herpes vaccine. They write about their findings in the 5 January online issue of the New England Journal of Medicine.

There is currently no cure or approved vaccine for genital herpes, a sexually transmitted disease caused by the viruses herpes simplex type 1 (HSV-1) and herpes simplex type 2 (HSV-2), with most infections thought to be caused by the latter (although a surprising finding of this study suggests that could be changing).

Genital herpes is one of the most common communicable diseases and affects about 1 in 4 women in the United States.

HSV-2 generally causes lesions and blisters in the genital area, and while HSV-1 generally causes sores in the mouth and lips, it has increasingly been found to cause genital disease.

Once inside the body, the virus stays for good. It can cause severe neurological disease, and even death in babies born to women infected with the virus, which is also a risk factor for sexual transmission of HIV.

In the NEJM study, the researchers report that an investigational vaccine developed by GlaxoSmithKline (GSK) provided partial protection agaist HSV-1 in a clinical trial involving more than 8,000 women at 50 sites in the US and Canada. The trial was funded by GSK and the National Institute of Allergy and Infectious Diseases (NIAID), which is part of the National Institutes of Health.

There were 58% fewer cases of HSV-1 in women who received the vaccine compared to women who received the control. It did not protect women against HSV-2.

In a note to the press, lead author Robert Belshe, director of the Center for Vaccine Development at Saint Louis University in Missouri, said:

"There is some very good news in our findings. We were partially successful against half of the equation -- protecting women from genital disease caused by HSV-1."

"It's a big step along the path to creating an effective vaccine that protects against genital disease caused by herpes infection. It points us in the direction to work toward making a vaccine that works on both herpes simplex viruses," he added.

Belshe and some of the other authors report having commercial relationships with GSK and other drug companies, such as receiving consultancy and lecture fees.

For the trial, they enrolled 8,323 women who were free of HSV-1 or HSV-2 infection. Their ages ranged from 18 to 32 at the start of the trial, and they were randomly assigned to receive either three doses of the vaccine or a control vaccine (one that prevents hepatitis A).

The researchers followed the participants for 20 months, monitoring for occurrence of gential herpes infection. During the trial, all participants also gave blood samples from which tests showed whether they were carrying HSV-1 or HSV-2 without showing symptoms.

The results showed that two of the three doses of the investigational vaccine offered protection against genital herpes from HSV-1. None offered protection against genital disease caused by HSV-2.

The authors summarize the results in their abstract:

"Overall, the vaccine was not efficacious; vaccine efficacy was 20% (95% confidence interval [CI], -29 to 50) against genital herpes disease. However, efficacy against HSV-1 genital disease was 58% (95% CI, 12 to 80). Vaccine efficacy against HSV-1 infection (with or without disease) was 35% (95% CI, 13 to 52), but efficacy against HSV-2 infection was not observed (-8%; 95% CI, -59 to 26)."

Belshe, who also is a professor of infectious diseases and immunology at St Louis, said they were surprised by the findings:

"We didn't expect the herpes vaccine to protect against one type of herpes simplex virus and not another. We also found it surprising that HSV-1 was a more common cause of genital disease than was HSV-2."

It has been suggested that HSV-1, once thought to cause mainly oral disease, is increasingly becoming a cause of genital disease because couples are engaging in oral sex.

Belshe explained that both HSV-1 and HSV-2 spread through direct contact, for instance from mouth to mouth, genitals to genitals, and mouth to genitals, even when infected persons have no symptoms.

The researchers are continuing to investigate why the vaccine only protected women against HSV-1 and not HSV-2. They are conducting tests on serum donated by the study participants.

Belshe suggests one reason could be that HSV-1 is more vulnerable to antibodies than HSV-2.