NIAID scientists have completed their study of a genetically engineered vaccine against herpes simplex virus type 2 (HSV-2). Although the vaccine proved to be safe and induced an immune response in the vaccinated volunteers, the vaccine did not protect HSV-negative recipients exposed to their infected partners. At present, neither Chiron Corp., the vaccine’s manufacturer, nor the NIAID researchers have determined why the vaccine was ineffective.
This vaccine was in development for nearly a dozen years. It worked extremely well as a preventive and as a treatment in several different species of experimental animals.
NIAID was the first to evaluate the vaccine in humans. In very carefully designed studies, NIAID researchers determined the vaccine’s safety, then went on to do dose-ranging studies and immune-response studies. They also completed two placebo-controlled studies to see whether vaccination would reduce outbreaks in people already infected. The vaccine did reduce the outbreaks by about 30 percent (similar to the effectiveness of the antiviral acyclovir), but that was less reduction than expected. More needs to be known about the human immune response to herpes before NIAID can initiate new vaccine or treatment studies.
Many People with Genital Herpes Don’t Have Outbreaks. Why?
To understand why the vaccine did not work in people, NIAID is redirecting its efforts back to basic research. The researchers will be studying the immune responses of people with herpes. People who have frequent HSV-2 outbreaks are being compared to HSV-2-infected volunteers who have no symptoms. One basic question is, what immune mechanisms protect people with asymptomatic herpes?
In the process, scientists hope that these studies will answer questions about the vaccine – for example, whether the vaccine induced the "right" immune response. The vaccine induced high-level responses of the types we know how to measure, but there may be other, as yet undefined, immune responses that the vaccine did not stimulate effectively.
The researchers also asked the vaccine to do something that traditional vaccines do not do. The measles vaccine, for example, prevents a disease that people are exposed to relatively infrequently, and the measles virus is spread through the air in very small amounts. In contrast, HSV-2 is shed from infected partners very frequently and in high amounts. Moreover, the virus is "inoculated" right onto susceptible mucous membranes. It is possible that the immunity required to block that process is unachievable by traditional vaccines. Understanding the immune processes of people who do not get symptoms may provide important clues for furthering the development of vaccines and treatments.
To learn more about participating in NIAID’s current study, symptomatic and asymptomatic HSV-2-infected volunteers may call 301-496-1836.
NIAID, a component of the National Institutes of Health, supports research on AIDS, tuberculosis and other infectious diseases as well as allergies and immunology.
Prepared by:
Office of Communications
National Institute of Allergy and Infectious Diseases
National Institutes of Health
Bethesda, MD 20892
Public Health Service
U.S. Department of Health and Human Services
April 1997