Herpes Simplex Virus Vaccine Closer to Reality

There were less than half of the cases of genital herpes caused by HSV-1--58% fewer--in women who received the investigational vaccine compared to women who received the control vaccine.

“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,” said Robert Belshe, MD, director of the Saint Louis University Center for Vaccine Development (MO, USA) and lead author of the study. “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.”

Both HSV-1 and HSV-2 are part of the herpesvirus family. Typically, HSV-2 causes lesions and blisters in the genital area. HSV-1 typically causes sores in the lips and mouth, although it increasingly has been found to cause genital disease.

There currently is no cure or approved herpes vaccine to prevent genital herpes infection, which affects approximately 25% of women in the United States and is one of the most common communicable diseases. Once inside the body, HSV remains there forever. The virus can cause severe neurologic disease and even death in infants born to women who are infected with HSV and the virus is a risk factor for sexual transmission of HIV.

The clinical trial of an investigational genital herpes vaccine was funded by the US National Institute of Allergy and Infectious Diseases, which is part of the US National Institutes of Health (NIAID; Bethesda, MD, USA), along with GlaxoSmithKline (GSK; London, UK), and conducted at 50 sites in the United States and Canada. The study enrolled 8,323 women between ages 18 and 30 who did not have HSV-1 or HSV-2 infection at the start of the study. They were randomly assigned to receive either three doses of the investigational HSV vaccine that was developed by GSK or a hepatitis A vaccine, which was the control.

Participants were monitored for 20 months and assessed carefully for occurrence of genital herpes disease. Moreover, all study participants were given blood tests to determine if asymptomatic infection with HSV-1 or HSV-2 occurred during the trial. The scientists discovered that two or three doses of the investigational vaccine offered significant protection against genital herpes disease caused by HSV-1. However, the vaccine did not protect women from genital disease caused by HSV-2.

“We were surprised by these findings,” said Dr. Belshe, who also is a professor of infectious diseases and immunology at Saint Louis University School of Medicine. “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.”

HSV-1 infection has become an increasingly common cause of genital disease, probably because more couples are engaging in oral sex. HSV-1 and HSV-2 are spread by direct contact--mouth to mouth, mouth to genitals, and genitals to genitals--even when the infected individual shows no symptoms, Dr. Belshe added. Researchers are conducting laboratory tests on serum obtained from study participants as they continue to study why the vaccine protected women from genital disease caused by HSV-1 and not HSV-2.

One theory according to Dr. Belshe, is that HSV-1 is more easily killed by antibodies than is HSV-2. This means that the vaccine antibodies might work better against HSV-1 and result in protection from HSV-1 but not HSV-2.

Earlier studies of the investigational herpes vaccines revealed it protected against genital herpes disease in women who were not infected with HSV-1 or HSV-2, but whose sexual partners were known to have genital herpes. Researchers believe the reason for the different outcome in the most recent clinical trial could be related to the fact that different populations were studied. The women in the earlier studies may have been protected due to immunologic or behavioral reasons not present in the later study.

“It’s always important to confirm scientific findings in repeated studies, which is why we investigated the vaccine in a large, placebo controlled trial,” Dr. Belshe concluded. “Our findings confirmed the validity of the scientific process. You’ve got to have good scientific evidence that something actually works.”

Related Links:
Saint Louis University Center for Vaccine Development